Patent ID: 12188323

DETAILED DESCRIPTION

An oil and gas well has a wellbore extending from a surface of the Earth to subterranean formations in the Earth. Sometimes, the wellbore can be under a body of water, for example, a sea or ocean. Such wellbores are referred to as a subsea wellbore. The subterranean formations contain liquid and gaseous phases of various fluids and chemicals including water, oils, and hydrocarbon gases. The wellbore conducts the fluids and chemicals from the subterranean formations to the surface. A subsea blowout preventer stack coupled to the subsea wellbore has annular preventers and rams to seal a flow of the fluids from the wellbore along a work string extending through the blowout preventer stack during wellbore drilling, completion, or workover operations. Sometimes, a pressure of the fluids in the wellbore and the subsea blowout preventer stack rapidly increases (a kick or surge), and the annular preventers and rams are operated to seal about the work string or sever the work string to seal the fluids in the wellbore from the surrounding environment.

The present disclosure relates to controlling a subsea blowout preventer stack, for instance, with a well control programmable logic controller responsive to conditions of the subsea blowout preventer system. In this approach, after a condition of the subsea blowout preventer stack is greater than a preset value, the well control programmable logic controller transmits a command signal to the annular preventers and/or the rams to seal the subsea blowout preventer stack.

FIG.1Ashows a well system having a subsea well control system controlling a subsea blowout preventer stack. The well system100has a wellbore102extending from a surface104of the Earth106. The Earth106has subterranean formations108which can contain liquid and gaseous phases of various fluids and chemicals including water, oils, and hydrocarbon gases. The wellbore102receives the fluids from the subterranean formation108and conducts the fluids to the surface104. A body of water110covers the surface104of the Earth106. For example, the body of water110can be a sea, an ocean, or a lake. In some cases, a typical water depth can range from about 150 meters to 3500 meters. The body of water110has a surface112. Above the surface112of the body of water110is an atmosphere114.

The well system100has a drill ship124floating on the surface112of the body of water110. Alternatively, the well system100could include a first generation to sixth generation semi-submersible rig or well intervention vessels. The drill ship124includes a rig126coupled to and extending upward from the drill ship124. A work string122is suspended from the rig126and extends from the rig126through the body of water110and into the wellbore102. The work string122can be a drill string to drill the wellbore102, a completion tool, a completion assembly, a landing string, a casing string, or a repair tool to perform a maintenance task on the wellbore102, a subsea test string, a tough logging condition (TLC) logging string (i.e., a wireline logging assembly on a drill pipe), or other well system100components.

The well system100has a subsea blowout preventer stack116coupled to the wellbore102at the surface104. The subsea blowout preventer stack116controls the flow of fluids from the wellbore102to the surface112of the body of water110. The work string122extends through the subsea blowout preventer stack116. The subsea blowout preventer stack116includes one or more annular preventers118and one or more rams120. The annular preventers118seal the fluids in the wellbore102. The annular preventer118seals about the work string122extending through the subsea blowout preventer stack116. The annular preventer118can seal against the work string122while the work string122rotates to prevent the fluid from flowing from the wellbore102through the subsea blowout preventer stack116into the body of water110, be used in a special case of volumetric stripping with work string122, or can be used to seal against an open hole where there is no work string122in the wellbore102during a well control event. The rams120can be a blind ran or a shear ram which can sever the work string122or sever and seal the subsea blowout preventer stack116to prevent the fluid from the wellbore102from flowing through the subsea blowout preventer stack116and into the body of water110. The rams120can be one or more of a pipe ram, a variable ram, a shear ram, a blind shear ram, or a casing ram. The rams120have an open position permitting the work string122to pass through the subsea blowout preventer stack116and a closed position sealing the subsea blowout preventer stack116. Moving from the open position to the closed position with the work string122positioned in the subsea blowout preventer stack116shears the work string122.

The well system100has a riser164extending from the subsea blowout preventer stack116to the drill ship124. The riser164is a hollow cylinder through which the work string122can pass to enter into the subsea blowout preventer stack116and a drilling mud can return from the wellbore102to the drill ship124(as described in more detail in reference toFIG.1B). Each section of the riser164(i.e, each riser joint) can support the combined weight of the subsea blow out preventer stack116and a lower marine riser package160(described in more detail below). However, in deep-water or ultra-deep water depths or applications, the riser164hanging weight is reduced by the attachment of a buoyant material (not shown) to an exterior of the riser joint164. The riser164systems can also include a telescopic joint (not shown) and multiple flex joints192in upper or lower locations with an electronic riser angle measurement system (not shown) which can be used to detect drill ship124offset from the riser164at different environmental load conditions. The flex joints192can articulate with drill ship124movement.

The well system100has a subsea blowout preventer control system128coupled to the subsea blowout preventer stack116and the annular preventer118and the rams120. The subsea blowout preventer control system128operates the annular preventer118and the rams120to seal the fluids in the wellbore102. The subsea blowout preventer control system128receives command signals from the drill ship124to operate the annular preventer118and the rams120. The subsea blowout preventer control system128has two control pods: an active control pod130a(also referred to as a blue pod) and a redundant control pod130b(also referred to as a yellow control pod). The control pods130a,130bhave a series of control valves132which direct hydraulic fluid to and from the annular preventer118and the rams120to operate the annular preventer118and the rams120. The control pods130a,130breceive the command signals from the drill ship124and operate the control valves132. The control pods130a,130bcan operate one or more of the annular preventer118and the rams120at a time, that is, simultaneously or sequentially, and in any order depending on the command signal.

The subsea blowout preventer control system128has a central control unit134mounted on the drill ship124. The central control unit134has various valves (such as pilot valves) and electronic control units (not shown) to receive, control, and transmit command signals to the control pods130a,130bvia a multiplex cable136wrapped around and deployable from a multiplex cable reel138mounted on the drill ship124. The multiplex cable136is coupled to the central control unit134and the control pods130a,130b. The multiplex cable136can transmit electronic or hydraulic control command signals. The central control unit134is positioned on the drill ship124. However, in some cases, for example, in shallow water depths, rather than a multiplex cable136, a hydraulic hose bundle (not shown) or umbilical (not shown) can be used to connect the central control unit134to the subsea control pods130a,130b.

The subsea blowout preventer control system128has a hydraulic fluid sub-system140to supply pressurized hydraulic fluid to the control pods130a,130b. The hydraulic fluid sub-system140has a blowout preventer fluid reservoir142. The blowout preventer fluid reservoir142has a fluid concentrate reservoir144and a mixed fluid reservoir146fluidly coupled to the fluid concentrate reservoir144. The fluid concentrate reservoir144contains a hydraulic fluid concentrate (typically in liquid form). The fluid concentrate reservoir144feeds the hydraulic fluid concentrate to the mixed fluid reservoir146. The mixed fluid reservoir146receives the hydraulic fluid concentrate from the fluid concentrate reservoir144and mixes the hydraulic fluid concentrate with a liquid, for example, with water or potable water from the drill ship124. The hydraulic fluid sub-system140is positioned on the drill ship124.

The hydraulic fluid sub-system140has a high pressure unit148to increase a pressure of the hydraulic fluid. The high pressure unit148receives the hydraulic fluid from the blowout preventer fluid reservoir142. The high pressure unit148has compressors150to pressurize the hydraulic fluid. The high pressure unit148is positioned on the drill ship124.

The hydraulic fluid sub-system140has a surface accumulator152to store the pressurized hydraulic fluid. The surface accumulator152receives the pressurized hydraulic fluid from the high pressure unit148. In response to the control valves132opening, the surface accumulators152supply the pressurized hydraulic fluid through the control pods130a,130bto the annular preventer118and/or one or more of the rams120, depending on the control valve132operated, to seal the subsea blowout preventer stack116.

The hydraulic fluid sub-system140has subsea accumulator154to store pressurized hydraulic fluid as a backup or emergency supply of pressurized hydraulic fluid for the control pods130a,130bto operate the annular preventer118and/or one or more of the rams120in the event of a failure of one or more components of the hydraulic fluid sub-system140. The subsea accumulator154is positioned the surface104of the Earth106.

The subsea blowout preventer control system128has a mini panel156and a main blowout preventer panel158operatively coupled to the hydraulic fluid sub-system140and the control pods130a,130bto supply pressurized hydraulic fluid through the control valves132in the control pods130a,130bto operate the annular preventer118and/or one or more of the rams120. The mini panel156and the main blowout preventer panel158are positioned on the drill ship124. The mini panel156and the main blowout preventer panel158each contain various switches and buttons to transmit the command signals to the central control unit134and subsequently to the control pods130a,130bvia the multiplex cable136to operate the annular preventer118and/or one or more of the rams120. The mini panel156and the main blowout preventer panel158have gauges and alarms which visually and audibly represent well system100conditions. In some cases, the alarms include the alarm a sounding alarm, a flashing light, or a speed dial call to an operator. The mini panel156and the main blowout preventer panel158can be manually operated by the operator on the drill ship124.

The well system100has a lower marine riser package160coupled to a bottom of the riser164as well as connected to the subsea blowout preventer stack116. The control pods130a,130bare coupled to and position within the lower marine riser package160. The lower marine riser package160provides structural support and protection to the subsea blowout preventer stack116. The lower marine riser package160also includes an emergency disconnect package (EDP) which provides a means to disconnect the riser system from the lower marine riser package160and the subsea blowout preventer stack116and is able to ensure that the drill ship124, a semi-submersible (not shown), or a well intervention vessel and riser164system is isolated from the subsea well environment (body of water110is an atmosphere114) in case of either a planned or an unplanned emergency disconnect. The unplanned emergency disconnect is not limited to a drift off, a drive off, a severe weather condition, or a loss of power. The emergency disconnect package can function and disconnect even under severe load conditions such as extreme weather conditions combined with high flex joint192angles. The emergency disconnect package can be function tested on a routine basis.

The well system100has multiple tensioners162which are adjustable via hydraulic pressure between an upper tension threshold limit and a lower tension threshold limit to couple the riser164to the drilling ship124. The tensioners162maintain bolts (not shown) fastening the riser164to the drill ship124in a state of tension.

The well system100has multiple sensors166positioned through out to sense conditions of the well system100. The sensors166transmit signals representing values of the conditions of the well system100. The conditions of the well system100sensed by the sensors166can include one or more of a temperature, a pressure, a fluid type of a fluid in the subsea blowout preventer stack116, a specific gravity of the fluid, a flow rate of the fluid, a position of a tool joint168of the work string122within the blow out preventer stack116, a location of the annular preventers118, a location of rams120, a position of the annular preventers118, a position of the rams120, a wear measurement of the annular preventers118, a wear measurement of the rams120, a closure blockage of at least one annular preventer118or the rams120, or a pressure of the subsea blowout preventer control system128. In some cases, the sensors166are one or more of a solid state magnetic field sensor, a Hall effect sensor, a strain gauge, or a proximity sensor to sense a position of a piston rods which moves in response the hydraulic fluid to operate the rams120or the annular preventer118. In other cases, the sensors166can be pressure sensor, temperature sensors, viscosity sensors, flow meters, or angle sensors which can detect an angle of the upper flex joints192or the lower flex joints192.

The lower marine riser package160also includes sensors166. The sensors166on the lower marine riser package160can sense the conditions of the lower marine riser package160including condition a loss of power to the lower marine riser package160, a loss of signal pilot valves (not shown, which control hydraulic fluid flow) of the lower marine riser package160, a loss of dynamic positioning, loss of hydraulic pressure to the subsea control pods130a,130b, an emergency disconnect signal to the emergency disconnect package, latching signals to the lower marine riser package160in case of reconnection, sensors on the thrusters (not shown) can detect a loss of dynamic positioning, a drift off, a drive off, a collision with a supply vessel (not shown), an electronic riser164angle exceeding a maximum design rating triggering the lower marine riser package160to disconnect from the subsea blowout preventer stack116.

The well system100includes a well control programmable logic controller170and an input/output device172. In some implementations, the well control programmable logic controller170is positioned with in the input/output device172. In some implementations, the well control programmable logic controller170and the input/output device172are both positioned in the drill ship124, however, in other implementations, one or both of the well control programmable logic controller170and the input/output device172are located in a offsite remote operations center (not shown) and the command signals are transmitted from the well control programmable logic controller170to the central control unit134on the drill ship124. The well control programmable logic controller170is operatively coupled to the subsea blowout preventer control system128to control the annular preventers118and the rams120. The operation can control inputs into the well control programmable logic controller170and view outputs, status, and conditions of the well control programmable logic controller170by the input/output device172. The well control programmable logic controller170performs operations including receiving the signal indicating the value of the conditions of the well system100from the sensors166; comparing the value to a preset value stored in the well control programmable logic controller170; and in response to the value greater than or equal to the preset value, transmitting a command signal to the subsea blowout preventer control system128to seal, by one or more of the annular preventers118and the rams120, the fluid flow through the subsea blowout preventer stack116. The operations of the well control programmable logic controller170are described in detail in reference toFIG.1C.

The well control programmable logic controller170includes a computer. The well control programmable logic controller170can be various forms of digital computers, such as printed circuit boards (PCB), processors, digital circuitry, or otherwise parts of a fracture geometry mapping system. Additionally, the system can include portable storage media, such as, Universal Serial Bus (USB) flash drives. For example, the USB flash drives may store operating systems and other applications. The USB flash drives can include input/output components, such as a wireless transmitter or USB connector that may be inserted into a USB port of another computing device.

The well control programmable logic controller170can include a processor174, a memory176, a storage device178, and the input/output device172can be interconnected using a system bus180. The processor174is capable of processing instructions for execution within the well control programmable logic controller170. The processor174may be designed using any of a number of architectures. For example, the processor may be a CISC (Complex Instruction Set Computers) processor, a RISC (Reduced Instruction Set Computer) processor, or a MISC (Minimal Instruction Set Computer) processor.

In one implementation, the processor174is a single-threaded processor. In another implementation, the processor174is a multi-threaded processor. The processor174is capable of processing instructions stored in the memory176or on the storage device to display graphical information for a user interface on the input/output device.

The memory176stores information within the well control programmable logic controller170. In one implementation, the memory176is a computer-readable medium. In one implementation, the memory176is a volatile memory unit. In another implementation, the memory176is a non-volatile memory unit.

The storage device178is capable of providing mass storage for the well control programmable logic controller170. In one implementation, the storage device178is a computer-readable medium. In various implementations, the storage device may be a floppy disk device, a hard disk device, an optical disk device, or a tape device.

The input/output device172provides input/output operations for the well control programmable logic controller170. In one implementation, the input/output device172includes a keyboard182and/or a pointing device184. In another implementation, the input/output device172includes a display device186for displaying graphical user interfaces.

The features described in respect to the well control programmable logic controller170can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. The apparatus can be implemented in a computer program product tangibly embodied in an information carrier, for example, in a machine-readable storage device for execution by a programmable processor; and method steps can be performed by a programmable processor executing a program of instructions to perform functions of the described implementations by operating on input data and generating output. The described features can be implemented advantageously in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. A computer program is a set of instructions that can be used, directly or indirectly, in a computer to perform a certain activity or bring about a certain result. A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment.

Suitable processors174for the execution of a program of instructions include, by way of example, both general and special purpose microprocessors, and the sole processor or one of multiple processors of any kind of computer. Generally, the processor174will receive instructions and data from a read-only memory or a random-access memory or both. The essential elements of a computer are a processor for executing instructions and one or more memories for storing instructions and data. Generally, a computer will also include, or be operatively coupled to communicate with, one or more mass storage devices for storing data files; such devices include magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits).

To provide for interaction with a user (the operator), the features can be implemented on a computer having the display device186such as a CRT (cathode ray tube) or LCD (liquid crystal display) monitor for displaying information to the user and a keyboard182and the pointing device184such as a mouse or a trackball by which the user can provide input to the computer. Additionally, such activities can be implemented via touchscreen flat-panel displays and other appropriate mechanisms.

These features can be implemented in a control system that includes a back-end component, such as a data server, or that includes a middleware component, such as an application server or an Internet server, or that includes a front-end component, such as a client computer having a graphical user interface or an Internet browser, or any combination of them. The components of the system can be connected by any form or medium of digital data communication such as a communication network. Examples of communication networks include a local area network (“LAN”), a wide area network (“WAN”), peer-to-peer networks (having ad-hoc or static members), grid computing infrastructures, and the Internet.

In some implementations, the well control programmable logic controller170includes a trip tank202volume monitoring module188, described in detail in reference toFIGS.1A and1B. In some implementations, the well control programmable logic controller170includes a real time inflow test module190, described in detail in reference toFIGS.1A and1B.

FIG.1Bshows a drilling mud system coupled to the well system ofFIG.1A. The well system100includes a drilling mud system200positioned in the drill ship124and coupled to the riser164and the work string122to control a flow of drilling mud through the wellbore102. The drilling mud system200has a trip tank202containing a volume of the drilling mud. The volume of the drilling mud is tracked during movement of the work string122. The drilling mud system200has a mud tank216(also referred to as a mud pit) in the drill ship124containing a larger volume of the drilling mud which flows down the work string122into the wellbore102.

The drilling mud system200has a trip tank pump204positioned in a fill up line206(also referred to as a surface line) fluidly coupling the trip tank202to the work string122. The trip tank pump204pressurizes and flows the drilling mud from the trip tank202to an annulus (not shown) defined by an inner surface the wellbore120and the riser164and an outer surface of the work string122. The drilling mud then flows out the work string122and through the annulus to a return line208which conducts the drilling mud back to the trip tank202during movement (tripping) of the work string122.

The drilling mud system200includes a float210resting on a surface212of the drilling mud in the trip tank202. The float210moves with the surface212of the drilling mud. A trip tank level indicator214is coupled to the float210and displays a trip tank202level (or corresponding volume) on the main blowout preventer panel158.

The drilling mud system200includes multiple sensors166positioned throughout the drilling mud system200. The sensors166positioned in the drilling mud system200transmit signals representing values of the conditions of the drilling mud system200to the well control programmable logic controller170. The conditions of the drilling mud system200sensed by the sensors166can include one or more of a flow rate of the drilling mud in the surface line206, a pressure of the drilling mud in the surface line206, a level of the drilling mud in the mud pit216, a volume of drilling mud in the mud pit216, a mud weight of the drilling mud, a level of drilling mud in a trip tank of the mud system, and a volume of drilling mud in the trip tank. The well control programmable logic controller170receives the signals representing the values of the conditions of the drilling mud system200and performs various operations described in reference toFIG.1C.

FIG.1Cis module view300of the well control programmable logic controller170ofFIG.1A. The well control programmable logic controller170receives the signals representing the values of the conditions of the well system100including the drilling mud system200and compares the values to preset values stored in the well control programmable logic controller170. Based on the result of the comparison, between the sensed values and the preset values, the well control programmable logic controller170operates the annular preventer118and the rams120.

The well control programmable logic controller170receives the signals representing the values of the conditions of the well system100from the sensors166. The well control programmable logic controller170has various modules which store the preset values for each condition, receive the values representing the conditions of the well system100, compare the values representing the conditions of the well system100to the preset values, and based on the result of the comparisons, operate the annular preventer118and rams120. The conditions of the annular preventer118and the rams120include a subsea annular preventer location indication302, a subsea shear/blind or shear rams location indication304, a subsea pipe rams location indication306, and a subsea blowout preventer pressure & temperature measurement308. The conditions of the subsea blowout preventer stack116include a fluid composition310and a tool joint position312. The conditions of the lower marine riser package160include a lower marine riser package tensioner314condition. The conditions of the subsea blowout preventer control system128include a subsea blowout preventer equipment emergency shut in/shear system status316, a subsea blowout preventer hydraulic control unit & pilot pressure measurement318, a subsea blowout preventer hydraulic unit flow measurement320, a surface & subsea accumulator charge and pressure system status322, and an actuator line flow measurement324.

The conditions of the drilling mud system200include, at the surface, an active mud pit level326, a return flow rate328, and a trip/strip tank level330. The conditions of the drilling mud system200include, at a subsea location, a feedback pressure & temperature332, and a feedback fluid type and specific gravity334. The subsea conditions of the well system100include a subsea lower marine riser tensioner feedback336and a subsea real time riser angle measurement338.

The values of the conditions302-338input into an input subsea module378and processes the values. The input subsea module378transmits the processed values of the conditions302-338to the processor174(a central processing unit), the memory176, and the storage device178. The processor174performs the following functions340-376including drift off analysis for the drilling riser164system on a mobile drilling unit. The processor174can be integrated with a dynamic positioning system on the rig126which can evaluate the position of the drill ship124under various wind and current speeds, wave heights, and wave periods. The processor174can determine the load or stress equivalent of the riser164and key riser164component real time conditions and make a comparison with preset data in the memory176. This can ensure a proper stroke-out of the tensioner162or telescopic joint, upper flex joint192limits and lower flex joints192limits, a wellhead connector condition, a lower marine riser package160connector (not shown) condition, or the riser164joints are all within acceptable limits. However, in some cases, where a limit (a threshold value) is exceeded on any component of the riser164system, the processor174can calculate ta allowable disconnect offset for the different components and identify a point of disconnect which can correspond to the smallest allowable disconnect for critical components of the riser164.

At step340, the processor174monitors for an input signal lost or a loss of pilot can include a loss of fluid sent to the pilot valves in the subsea control pods130a,130bfor the hydraulic blow out preventer stack control system128or in deeper waters where umbilical handling and reaction time would be so large such that it is impractical. The loss of pilot can include a loss of either electric signals which operate solenoid vales and/or loss of hydraulic signal from the solenoid valves to the respective pilot valve in the subsea control pods130a,130b. In some cases, an acoustic system (not shown) is used to control the subsea blow out preventer stack116and the loss of pilot can be a loss of acoustic signals. The processor174monitors for a loss of power signal. In response to a NO condition at340, the processor174moves to step342.

At step342, the processor174compares the subsea blowout preventer pressure and temperature measurement308to a preset subsea blowout preventer pressure temperature measurement. The processor174monitors for a condition where the subsea blowout preventer pressure and temperature measurement308is greater than or equal to the preset subsea blowout preventer pressure temperature measurement. In response to the subsea blowout preventer pressure and temperature measurement308less than the preset subsea blowout preventer pressure temperature measurement, i.e., a NO condition, the processor174provides a feedback adjustment to the subsea feedback pressure & temperature332and the functions restart at step340. In response to the subsea blowout preventer pressure and temperature measurement308greater than or equal to the preset subsea blowout preventer pressure temperature measurement, i.e., a YES condition, the processor174moves to step344.

At step344, the processor174compares the fluid composition310(i.e., a fluid type by average specific gravity) to a preset value of specific gravity for fluid types. Monitoring the specific gravity can indicate or detect a complete loss of well control where the well has been displaced with an influx or where there is reduced density as a result of the influx. The fluid type and pressure and temperature from step342can provide a positive indication of loss of well control. Early intervention can help to prevent the riser164from unloading. The processor174monitors for a condition where the fluid composition310(i.e., specific gravity) is less than the specific gravity preset value (preset gravity includes the mud density and impact of temperature and pressure with a tolerance included). In response to the fluid composition310(i.e., specific gravity) equal to or greater than the specific gravity preset value, i.e., a NO condition, the processor174provides a feedback adjustment to the subsea feedback fluid type & specific gravity334and the functions restart at step340. In response to the fluid composition310(i.e., specific gravity) less than the specific gravity preset value and correlates with fluid type and specific gravity of influx from different horizons as well as the pressure and the temperature greater than or equal to the preset value, and memory176includes specific gravity of several combinations of influx and mud up to fully displaced influx for all the exposed producible hydrocarbon intervals and position, i.e., a YES condition, the processor174moves to step346.

At step346, the processor174monitors the tool joint position312for a condition where tool joint position312is in the subsea blowout preventer stack116. In response to the tool joint position312outside the ram position in the subsea blowout preventer stack116, i.e., a NO condition, the processor174moves to step348. At step348, the processor174activates the subsea emergency shear system (the rams120) by sending a signal to the well control module output350, which, at step352, closes the subsea blowout preventer shear rams & activates a relay, and moves to step354.

At step354, the processor174confirms the subsea shear ram function. In response to confirming proper operation and function of the subsea shear ram, i.e. a YES condition, the processor174moves to step356. At step356, the processor174transmits a command signal to close the subsea blind rams and moves to step358. At step358, the processor174confirms blind ram function and proceeds to step360. At step360, the processor174confirms lower marine riser package tensioner with limits. For example, the processor174can compare the lower marine riser package tensioner314between the upper preset value threshold and the lower preset value threshold. In response to the value of the tension of the lower marine riser package tensioner314greater than the upper preset value threshold or less than the lower preset value threshold, the processor174moves to step362. At step362, the processor174initiates a sound or flashing light alarm and disconnects the lower marine riser package160and the riser164from the drill ship124and the processor174stops.

Returning to step340, in response to a YES condition at step340, the processor moves to step364. At step364, the processor174monitors the tool joint position312for a condition where tool joint position312is in the subsea blowout preventer stack116. In response to the tool joint position312not within the ram position in the subsea blowout preventer stack116, i.e., a NO condition, the processor174moves to step348. At step348, the processor174activates the subsea emergency shear system (the rams120) by sending a signal to the well control module output350, which, at step352, closes the subsea blowout preventer rams & activates a relay, and moves to step354. At step354, the processor174confirms the subsea shear ram function. In response to confirming proper operation and function of the subsea shear ram, the processor174moves to step356. At step356, the processor174transmits a command signal to close the subsea blind rams and moves to step358. At step358, the processor174confirms blind ram function and proceeds to step360. At step360, the processor174confirms the lower marine riser package tensioner with limits. For example, the processor174can compare the lower marine riser package tensioner314between the upper preset value threshold and the lower preset value threshold. In response to the value of the tension of the lower marine riser package tensioner314greater than the upper preset value threshold or less than the lower preset value threshold, the processor174moves to step362. At step362, the processor174initiates a sound or flashing light alarm and disconnects the lower marine riser package160and the riser164from the drill ship124and the processor174stops.

Returning to step346or364, in response to the tool joint position312within the subsea blowout preventer stack116, i.e., a YES condition, the processor174moves to step366. At step366, the processor174actives a subsea emergency shut-in system and moves to step368. At step368, in response to the processor174activating the subsea emergency shut-in system, the well control module of the processor174generates an output, i.e., the processor174transmits a command signal to the annular preventer and a lower ram and moves to step370.

At step370, the processor174closes the annular preventer on the lower marine riser package160or the subsea blowout preventer stack116and moves to step372. At step372, the processor confirms shut-in of the annular preventer118and the lower ram120and moves to step374. At step374, the processor174confirms the lower marine riser package tensioner with limits. For example, the processor174can compare the lower marine riser package tensioner314between the upper preset value threshold and the lower preset value threshold. In response to the value of the tension of the lower marine riser package tensioner314greater than the upper preset value threshold or less than the lower preset value threshold, the processor174moves to step362. At step362, the processor174initiates a sound or flashing light alarm and disconnects the lower marine riser package160and the riser164from the drill ship124and the processor174stops.

Returning to step354, the processor174confirms the subsea shear ram function. In response to confirming an improper operation and a dis-function of the subsea shear ram, i.e. a NO condition, the processor174moves to step370. At step370, the processor174closes the annular preventer on the lower marine riser package160or the subsea blowout preventer stack116and moves to step372. At step372, the processor confirms shut-in of the annular preventer118and the lower ram120and moves to step374. At step374, the processor174confirms the lower marine riser package tensioner with limits. For example, the processor174can compare the lower marine riser package tensioner314between the upper preset value threshold and the lower preset value threshold. In response to the value of the tension of the lower marine riser package tensioner314greater than the upper preset value threshold or less than the lower preset value threshold, the processor174moves to step362. At step362, the processor174initiates a sound or flashing light alarm and disconnects the lower marine riser package160and the riser164from the drill ship124and the processor174stops.

The operation of the rams120can be staggered or delayed. A subsea blowout preventer stack116and subsea blowout preventer control system128can have a delay time controlled by the well control programmable logic controller170. The delay time is predetermined by the operator. In some cases, the predetermined delay time is twice a response time required to seal the subsea blowout preventer stack116. In other cases, the predetermine delay time is twice a response time required to activate the at least one ram120.

The delay time is between the activation of the first ram120(a subsea blowout preventer shear ram) and the activation of the second ram120(one or more sealing rams). The delay is built into the well control programmable logic controller170is based the measurement of the position of a piston of the subsea blowout preventer shear rams120when the rams120are activated and functioning properly. The logic of the well control programmable logic controller170assesses the shear criteria (a shear preset value) programmed in the well control programmable logic controller170which monitors the shearing pressure and fluid volume required to shear the work string122in the subsea blowout preventer stack116and compares with the calculated shear pressure for the work string122.

The sequence for the secondary seal (another annular preventer118or another ram120) will only be activated after a preset period determined by the operator and programmed in the well control programmable logic controller170responsive to the criteria being met and the location sensor166on the shear rams120confirms full stroke of the shear ram piston (i.e. full tubular shear). Responsive to full stroke of the shear ram piston is not confirmed, the sealing ram120will not be activated. When the sealing ram120is activated, the well control programmable logic controller170monitors the function of the ram120and confirms that the wellbore102is effectively sealed.

In some implementations, referring toFIGS.1A and1B, the well control programmable logic controller170includes the trip tank202volume monitoring module188. The well control programmable logic controller170monitors of the volume of the trip tank202with the calibrated trip tank level indicator214and output display on main blowout preventer panel158. For example, the trip tank level indicator214can show the level of the trip tank202relative to time during a flow check operation. The well control programmable logic controller170can detect any change in trip tank202volume by comparing the trip tank202volume or level to a trip tank202threshold volume or threshold level during the period of the flow check operation and send a signal to the main blowout preventer panel158which could be electric, hydraulic, pneumatic or a combination, signifying a positive indication of inflow (kick) into the wellbore102. The well control programmable logic controller170can detect the change in trip tank202volume or level during tripping operations. The well control programmable logic controller170can also provide positive indication of a swabbed in kick condition where the volume of a steel displacement being less than a calculated displacement while pulling the work string122out of the wellbore102or where the volume of displacement is greater than the steel displacement while tripping the work string122into the wellbore102. The well control programmable logic controller170can calculate the displacement volumes based on a bottom hole assembly configuration of the work string122.

In some implementations, referring toFIGS.1A and1B, the well control programmable logic controller170includes a real time inflow test module190. An inflow test can be conducted on the wellbore102by the well control programmable logic controller170by reducing a pressure of the subsea well control system, monitoring a flow rate from the subsea well control system, adjusting the flow rate for temperature effects, comparing the adjusted flow rate to a zero leak rate, and based on the result of the comparison, in response to the adjusted flow rate is great than or equal to the zero leak rate, determining that an inflow condition exists. The flow rate can be adjusted for temperature affects by an algorithm like the Horner Time to evaluate the test data to ensure it complies with the zero-leak-rate criteria. In some wellbores102which are high pressure high temperature wellbores, the real time inflow test module190can further identify and distinguish in real-time between fluid expansion due to temperature effects and actual formation fluid influx and detect wellbore102ballooning effects when drilling with mud weights close to a fracture gradient threshold.

FIG.2is a flow chart400of an example method of controlling a subsea blowout preventer stack. At402, a condition of a subsea blowout preventer stack and a subsea blowout preventer control system operatively coupled to the subsea blowout preventer stack is sensed. The condition can be at least one of a temperature, a pressure, a fluid type of a fluid in the subsea blowout preventer stack, a specific gravity of the fluid in the subsea blowout preventer stack, a flow rate in the subsea blowout preventer stack, a presence of a tool joint of a work string, a location of one or more annular preventers, a location of one or more rams, a position of the annular preventers, a position of the rams, a wear measurement of the annular preventers, a wear measurement of the rams, a closure blockage of at least one of the annular preventers or the rams, or a pressure of the subsea blowout preventer control system. For example, referring toFIG.1A, the conditions of the subsea blowout preventer stack116including the annular preventers118and the rams120can be is sensed.

At404, a signal representing a value of the condition is transmitted to a well control programmable logic controller operatively coupled to the subsea blowout preventer control system. For example, referring toFIG.1A, the sensors166transmit the values representing the conditions of the subsea blowout preventer stack116including the annular preventers118and the rams120are transmitted to the well control programmable logic controller170. The well control programmable logic controller170operates the subsea blowout preventer control system128.

At406, the signal is received at the well control programmable logic controller. For example, referring toFIG.1A, the well control programmable logic controller170receives the signals from the sensors166.

At408, the value is compared to a preset value. For example, referring toFIG.1C, the well control programmable logic controller170can compare the signals representing the conditions302-332are compared in steps340-346,354,358,364, and372-374.

At410, based on the result of the comparison, in response to the value greater than or equal to a preset value, a command signal is transmitted to the subsea blowout preventer control system to seal, by at least one of the annular preventers and the rams of the subsea blowout preventer stack, a fluid flow through the subsea blowout preventer stack. For example, referring toFIG.1C, the well control programmable logic controller170can transmit signals at steps350and368.

In some implementations, sealing the fluid flow through the subsea blowout preventer stack includes activating at least one ram to seal the subsea blowout preventer stack; after activating the ram, waiting a predetermined delay time; and after waiting the predetermined delay time, activating another ram or an annular preventer to further seal the subsea blowout preventer stack. In some cases, the predetermined delay time is twice a response time required to seal the subsea blowout preventer stack. In some cases, the predetermine delay time is twice a response time required to activate one ram. For example, the well control programmable logic controller170can operate the annular preventers118and the rams120with a delay time.

In some implementations, sealing the fluid flow through the subsea blowout preventer stack includes monitoring i) a shearing pressure of the ram, ii) a fluid volume required to shear the work string by the ram, and iii) a position of a shear ram piston of the ram. The method can include comparing the shearing pressure to a calculated shear pressure for the work string. The shearing pressure being greater than or equal to the calculated shear pressure indicates proper operation of the ram. The method includes comparing the fluid volume required to shear the work string to a calculated fluid volume required to shear the work string. The fluid volume required to shear the work string being greater than or equal to the calculated fluid volume indicates proper operation of the ram. The method includes detecting the position of the shear ram piston at a full stroke position indicating a full tubular shear of the work string. The method includes in response to i) the shearing pressure greater than or equal to the calculated shear pressure, ii) the fluid volume required to shear the work string greater than or equal to the calculated fluid volume, and iii) the position of the shear ram piston is at the full stroke position, waiting the predetermined delay time. The method includes after waiting the predetermined delay time, activating another ram to further seal the subsea blowout preventer stack. For example, the rams120can be operated with a delay time to verify proper operation as described in reference toFIG.1C, steps354,358, and370.

In some implementations, the method further includes receiving, from lower marine riser package sensors coupled to a lower marine riser package, where the lower marine riser package is coupled to and positioned about the subsea blowout preventer stack, a signal representing a value of a condition of the lower marine riser package. The condition can include at least one of a loss of power to the lower marine riser package, a signal to the emergency disconnect package to disconnect or latch, a loss of signal to pilot valves of the lower marine riser package, a loss of dynamic positioning, loss of hydraulic pressure to subsea control pods, a drift off, a drive off, a collision with the supply vessel, an electronic riser angle exceeding a maximum design rating triggering the lower marine riser package to disconnect from the subsea blowout preventer stack. The method can include comparing the value to a lower marine riser package and/or riser preset values. The method can include, based on the result of the comparison, in response to the value greater than or equal to a preset value, transmitting the command signal to the subsea blowout preventer control system to seal, by an annular preventer and rams of the subsea blowout preventer stack, a fluid flow through the subsea blowout preventer stack. In some cases, the method can further include adjusting a value of a tension of tensioners coupling the lower marine riser package to the subsea blowout preventer stack within an upper tension limit and a lower tension limit. For example, the tension in tensioners162can be monitored and adjusted by the subsea blowout preventer control system128.

In some implementations, the method further includes receiving, at the well control programmable logic controller, a signal representing a value of a condition of a mud system. The mud system flows a drilling mud to the subsea blowout preventer stack. The condition of the mud system can be at least one of a flow rate of the drilling mud in a surface line of the mud system, a pressure of the drilling mud in the surface line of the mud system, a level of the drilling mud in a mud pit of the mud system, a volume of drilling mud in the mud pit, a mud weight of the drilling mud, a level of drilling mud in a trip tank of the mud system, and a volume of drilling mud in the trip tank. The method can include comparing the value of the condition of the mud system to a mud system preset value. The method can include in response to the value greater than or equal to a corresponding mud system preset value, transmitting the command signal to the subsea blowout preventer control system to seal, by at the annular preventers and the rams of the subsea blowout preventer stack, a fluid flow through the subsea blowout preventer stack. For example, the trip tank202volume monitoring module188monitors of the volume of the trip tank202with the calibrated trip tank level indicator214with and output display on main blowout preventer panel158.

In some implementations, the method further includes, by the well control programmable logic controller, reducing a pressure of the subsea well control system; monitoring a flow rate from the subsea well control system; adjusting the flow rate for temperature effects; comparing the adjusted flow rate to a zero leak rate; and based on the result of the comparison, in response to the adjusted flow rate is great than or equal to the zero leak rate, determining that an inflow condition exists. For example, the real time inflow test module190can perform the inflow test on the wellbore102by monitoring the flow rate from the subsea well control system, adjusting the flow rate for temperature effects, comparing the adjusted flow rate to a zero leak rate, and based on the result of the comparison, in response to the adjusted flow rate is great than or equal to the zero leak rate, determine that the inflow condition exists.

In some implementations, the method further includes receiving, at the well control programmable logic controller, a control signal from an offsite real-time operations center; and transmitting, to the offsite real-time operations center and from the well control programmable logic controller, a status signal indicating the condition of the subsea well control system. For example, the well control programmable logic controller170can transmit status signals to and receive command signals from an offsite real-time operations center.

Although the following detailed description contains many specific details for purposes of illustration, it is understood that one of ordinary skill in the art will appreciate that many examples, variations, and alterations to the following details are within the scope and spirit of the disclosure. Accordingly, the example implementations described herein and provided in the appended figures are set forth without any loss of generality, and without imposing limitations on the claimed implementations.