Method and apparatus for selecting diversion material for a wellbore operation

Diversion material is particulate material used during wellbore treatment to temporarily seal a wellbore fluid passage such as a fracture. A method and apparatus for diversion material testing permits simulation of wellbore fracture parameters and testing thereof against a selected diversion material. The apparatus comprises: a fluid piping system including a fluid inlet end and a fluid outlet end; a fracture simulator chamber including a fracture-simulating outlet slot through a wall of the chamber, the fracture simulator chamber being releasably connectable to the fluid outlet end; a pump to pump fluid through the fluid piping system from the fluid inlet line to the fluid outlet end and into the fracture simulator chamber; a diversion material launch system connected in communication with the fluid piping system between the fluid inlet end and the fluid outlet line; and a pressure transducer in the fluid piping system to measure pressure in the fluid piping system.

FIELD OF THE INVENTION

The present invention relates to methods and apparatus and, in particular, for selection and testing of diversion material.

BACKGROUND

Diversion material is a particulate material used during wellbore treatment operations to temporarily seal a fluid passage, such as a fracture in a wellbore operation. In particular, diversion material may be conveyed downhole and placed against or within a fluid passage to create a seal against the fluid passage. The diversion material is selected to be slightly soluble in wellbore conditions such that with residence time downhole, the seal created by the diversion material solubilizes to reopen the fluid passage. The solubilized diversion material can then be produced back. Diversion material is sometimes referred to as diverter, a bridging agent, a temporary degradable particulate or solid production chemical.

Diversion material is entrained in wellbore treatment fluids and it is intended to be forced into wellbore fractures to prevent fluid loss to that area of the wellbore. Diversion material is available in different particle sizes and shapes, often categorized by mesh size. Diversion material is also available with different degradation properties based to residence time and wellbore conditions temperature.

Diversion material testing is difficult and oftentimes the testing is done directly in the wellbore. In-wellbore testing is not ideal, as it is less difficult to validate performance, technology and treatment plans.

SUMMARY

The invention relates to methods and apparatus for testing of diversion material for wellbore applications.

In accordance with a broad aspect of the invention, there is provided an apparatus for testing wellbore materials comprising: a fluid piping system including a fluid inlet end and a fluid outlet end; a fracture simulator chamber including a fracture-simulating outlet slot through a wall of the chamber, the fracture simulator chamber being releasably connectable to the fluid outlet end; a pump to pump fluid through the fluid piping system from the fluid inlet line to the fluid outlet end and into the fracture simulator chamber; a diversion material launch system connected in communication with the fluid piping system between the fluid inlet end and the fluid outlet line; and a pressure transducer in the fluid piping system to measure pressure in the fluid piping system

In accordance with another aspect of the invention, there is provided a method for testing the efficiency of a diversion material with respect to a wellbore fracture profile comprising: injecting a diversion material with a known particle size through a test apparatus including through a fracture simulator; and monitoring pressure conditions in the test apparatus to identify an increase in pressure indicative of a fluid blockage formed in the fracture simulator by the diversion material

DETAILED DESCRIPTION OF THE VARIOUS EMBODIMENTS

The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments contemplated by the inventor. The detailed description includes specific details for the purpose of providing a comprehensive understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.

A fracture profile of a wellbore may be known including any one or more fracture parameters such as fracture dimensions such a fracture width, length or depth. Based on the type of formation (i.e. carbonate, shale, sandstone, etc.) it is possible to characterize another fracture profile parameter: surface roughness. The fracture orientation can also be established to determine another aspect of the fracture profile. The orientation may include parameters such as the number of fractures in an area and orientation of the fracture length relative to the wellbore axis (i.e. axially extending, circumferentially extending, etc.).

It has been determined that, depending on a fracture profile, some diversion material particle sizes work better than others. The present invention offers a method and apparatus for selecting and validating the usefulness of a diversion material or a selected series or blend of diversion materials for a particular fracture profile. An appropriate diversion material profile such as, for example, a diversion material chemical or particle size, a blend of diversion materials including with a particle size distribution, a series of diversion materials (i.e. a plan), an amount and/or a volume of diversion material may be determined for a particular fracture profile.

Alternately, the method and apparatus may be used to validate the suitability of new diversion materials, blends and program plans.

The apparatus can be operated in a manner to emulate wellbore conditions and launch conditions.

In one embodiment, a method and apparatus is provided to test the efficiency of a diversion material with respect to a selected fracture profile including a fracture size such as a fracture width.

In the method, a diversion material with a known particle size is injected at process conditions similar to, for example scaled to, known fracturing conditions through a test apparatus, including through a fracture simulator, while the process conditions in the test apparatus are monitored. The process conditions being monitored indicate the bridging of diversion material particles and the back pressure based on particle size.

A possible test apparatus10is shown inFIG. 1. Apparatus10includes a fluid piping system12including a fluid inlet end12aand a fluid outlet end12band a fracture simulator at the fluid outlet end12b.

With reference also toFIGS. 3aand 3b, fracture simulator14, includes therein a fracture simulator chamber14aand a fracture-simulating outlet slot16through a wall that defines the chamber. Fracture simulator14is releasably connectable, as by a releasable connection15to the fluid outlet end of the fluid piping system and is connected in fluid communication with the fluid piping system to receive fluid from the outlet end into the chamber14a.

As is typical for a slot, slot16has edges that define an opening in the shape of a rectangle with a length dimension L and a width dimension W, which is smaller than the length. This rectangular shape is useful to simulate a wellbore fracture, since a fracture also has a length and a width, where the width is smaller than the length. The slot characteristics, such as its dimensions and its orientation, can be defined and recorded for each fracture simulator, as will be appreciated by further description herein below. Apparatus10may have more than one fracture simulator14with differing slot dimensions and features. The releasable connection15facilitates installation and removal for interchanging simulators14on end12b.

The diameter of the sidewall14b,which thereby defines inner diameter across chamber14a,can be scaled based on hole dimensions. However, it is not necessary to duplicate the hole dimensions, as the process conditions can be accommodated to simulate wellbore fracturing conditions without using a fracture simulator that matches the hole inner diameter. While the best testing apparatus would have the same size as the wellbore casing/hole size in which the diversion material is to be employed, typically conditions within a larger diameter hole can be simulated adequately even using a smaller diameter fracture simulator.

The apparatus further includes a pump18to pump fluid through the fluid piping system from the fluid inlet end12ato the fluid outlet end12band into the fracture simulator's chamber14a.The pump is configured to pump fluid through piping12from source through the pump into fracture simulator14at rates scalable to rates employed in wellbore operations. For example, pump18is capable of operation to generate continuous flow and capable of inducing turbulence in fluid flow at least at fracture simulator. The method includes pumping at a rate, for example between 20-60 l/m, to induce turbulence in the fluid flowing through the fracture simulator to simulate the flow during wellbore fracturing operations. The pumping can be maintained continuously over a period of time for prolonged testing or to pump more than one pill.

A diversion material launch system20is connected in fluid communication with the fluid piping system between the fluid inlet end and the fluid outlet line. The diversion material launch system is configured to launch, arrow DV, diversion material into the fluid piping system so that it can be entrained in the fluid passing through the apparatus toward the fracture simulator. The diversion material launch system may take many forms, for example with supply tanks, injection mechanisms, etc. In one embodiment, system20introduces the diversion material by gravity, suction, back pressure, valving, etc. from a supply line20ainto fluid piping12.

A pressure transducer22in the fluid piping system is configured to measure pressure in the fluid piping system. Optionally, the apparatus may further include a flow meter23or and/or a controller such as a programmable logic controller (PLC)24. The flow meter and/or pressure transducer measure process conditions within the apparatus, for example, fluid conditions such as a flow rate and pressure. The PLC24can monitor overall conditions and feedback to the pump18, for example, to shut down the pump if pressure increases to a set level.

Apparatus10may include or receive connection to a fluid source26at the inlet end14a.Likewise, a fluid discharge28, such as may include a receptacle such as a pan or tank, can be provided to receive fluid passing from slot16of fracture simulator14. The fluid can be a fluid used in actual wellbore fracturing such as liquid (i.e. water, gel, hydrocarbon, etc.) or gas (i.e. nitrogen, hydrocarbon, etc.) Depending on the fluid being used and general apparatus operations, fluid may openly flow to discharge28or may be passed through a contained discharge line28a.To best simulate downhole fracture conductivity conditions, the discharge components28,28aare at some point open to ambient.

Apparatus10is configured to move fluid, arrow A, from the fluid inlet end to the fluid outlet end, to load an amount of a diversion material from the diversion material launch system into the fluid and to move the diversion material into the fracture simulator chamber, while monitoring the pressure for a pressure increase indicative of the diversion material blocking the fracture-simulating slot16.

In any test, one amount of diversion material, which is sometimes referred to as a “pil,” can be launched and pumped into the fracture simulator while pressure is monitored or a series of amounts (i.e. pills) of diversion material or other materials can be launched and monitored. In a test including series of pills, the pills of diversion material can all be the same type/concentration of diversion materials or all or some of the pills can be of other types.

Another test apparatus50is shown inFIG. 2. The apparatus is similar to that ofFIG. 1. However, apparatus50has options that can be employed each alone or in combination. Notable options include an in-line material launcher52and a by-pass loop52d.

In-line material launcher52includes a chamber52athat can accommodate diversion material and an inlet52bconnected to upstream fluid piping and an outlet52cconnected to downstream fluid piping. Process fluid can be introduced to the chamber via inlet52bto entrain the diversion material contained therein and then process fluid with entrained diversion material can exit the chamber and flow towards the fracture simulator14. Apparatus50can include a diversion material supply tank17connected by a line and valve to the launcher52. The diversion material can be loaded to the launcher from the supply tank17, permitting each pill in a series of pills to be prepared and can be loaded from supply tank17to chamber52aone at a time.

By-pass loop52dis a piping line that by-passes direct line54to the simulator and permits fluid communication with launcher52. Direct line54extends to provide communication between the inlet end and the outlet end of the piping12without passing through the launcher. Valves56a,56b,such as three-way valve56apermit selection of the fluid path either through direct line54or through by-pass loop and launcher52.

The apparatus contains three-way valve56aand fitting arrangement such that flow can either flow directly to the wellhead or by-pass to the diverter material launching section. Thus, in a method to pump fluid from fluid source26to fracture simulator14, the operator can establish a control, baseline pressure, arrow B, prior to reconfiguring the valve56ato permit flow through the diverter material launching section, arrow C, to launch diverter. In addition or alternately, valve56acan be actuated to direct flow through the direct line54when testing the effects of launching multiple pills in sequence. Flow can be continuous through the fracture simular by directing flow through the direct line54while the next pill is being loaded from tank17to launcher52. After the next pill is loaded, valve56acan be selected to open flow through line52dto launcher52. Thus it is possible to pump pills on the fly in sequence until the desired performance result is achieved or the test is otherwise complete.

The apparatus, for example as shown inFIG. 1 or 2, permits the use of various fracture simulators to simulate wellbore fracture conditions. It is even noted that the fracture simulator14ofFIG. 1differs from that ofFIG. 2and there are even further options such as those shown inFIGS. 3a-5c.

The fracture simulator includes a releasable connection15at its inlet end through which it is securely but releasably connected in a pressure tight manner onto the outlet end of the piping. The releasable connection, for example, may be a threaded, quick release or flanged connection.

The releasable connection facilitates removal and replacement of one type of fracture simulator with another type. For example, one fracture simulator of a known geometry can be quickly replaced with another fracture simulator of a known but different geometry, for example each having a different slot width to each simulate a corresponding fracture width. In one embodiment, for example, an apparatus may include a plurality of fracture simulators each similar in many ways, for example with similar releasable connectors, length, inner diameter, but with different slot characteristics (i.e. dimensions, roughness or orientations). A fracture simulator may therefore be selected from the plurality of fracture simulators for installation onto the test apparatus based on desired slot characteristics against which the diversion material is to be tested. The selected slot characteristic such as width may be that to correspond with a known fracture condition, such as fracture width, such as according to the formation's fracture profile in which the diversion material to be tested is intended to be used.

As shown inFIGS. 2-3d, a basic fracture simulator14has a wall that defines therewithin a fracture simulator chamber14aand a fracture-simulating outlet slot16through the wall. The fracture simulator chamber is configured to define a flow path for fluid from its inlet end14b,along a long axis x and then substantially perpendicularly relative to axis x, toward the slot. As such, fluid passing through the chamber, arrow P, is redirected substantially perpendicularly from the long axis to pass through the fracture-simulating outlet slot16.

Typically, the fracture simulator chamber is defined within, as the inner diameter of, an elongate cylindrical tubular member. A side wall14dof the member defines an inner diameter and the long axis x extends between open end14band a closed end14cand the fracture-simulating outlet slot is positioned in the side wall. For example, the fracture simulator may be a length of pipe with an open end and an opposite closed end, with the inner diameter of the pipe forming the chamber14a.Slot16is on the pipe's side wall extending from, and thereby creating an opening, from the pipe's inner surface to its outer surface. As noted, the side wall location of the slot orients the slot as perpendicular to the long axis of the pipe's inner diameter, and thereby orients the slot as perpendicular to inlet flow into the fracture simulator chamber formed by its inner diameter.

The slot, being formed through the side wall, simulates the location of a fracture in a wellbore, wherein the fracture is located on the cylindrical wellbore wall.

With reference toFIGS. 3cand 3d, photographs show a successful diversion material seal established against a fracture simulator slot. Larger diameter diversion materials (i.e. bridging agent) are initially stopped by and pack against the slot16. After the larger diameter materials begin to bridge, then the finer diversion materials are stopped and pack against the bridging agent. Eventually, the diversion materials substantially stop fluid flow through the slot. The photos are from an actual test with one pill of diversion material. Since less than1cm fill was found on the bottom, the fracture simulator was operating properly with material caking on the sidewall at the slot, rather than filling the bottom. This also shows that volume of material was optimized with very little wasted product and the material creating a seal without packing the simulator chamber.

The embodiment shown inFIGS. 3a-3dtests the placement of a near wellbore seal. In particular, the diversion material is deposited on the sidewalls and in the slot, which has a minimal depth—only the thickness of the simulator wall.

For each fracture simulator, the slot characteristics, such as its dimensions L, W and orientation, are known. The width W of the slot can be selected to correlate to the width of a fracture from fracture simulation modelling. By selecting pump conditions, the response of diversion material with respect to slot16can be very similar to an actual wellbore response. In one embodiment, a plurality of fracture simulators, each having a slot width differing by 1 mm increments with widths between 1 mm and 11 mm. The slot is generally free of screen so that the bridging effect can be correlated to the slot characteristics.

The length L can be varied, but in one embodiment it is maintained standard since the fracture length has relatively lower impact on diversion material activity in wellbore operations than other slot characteristics such as width.

The orientation, which means placement and orientation of the length L relative to axis, can be also be varied.

For example, while only one slot16is shown the embodiment ofFIG. 3a, a fracture simulator may include more than one slot. To simulate a wellbore condition, in one embodiment, there may be a second slot similar to slot16but positioned diametrically opposed on the opposite sidewall. Such a condition in a wellbore, where fractures are diametrically opposed, is known as a bi-wing (or bi-planar) frac.

An embodiment with a bi-wing slot orientation is shown inFIGS. 4aand 4b. In this embodiment, fracture simulator60includes two slots62diametrically opposed across the diameter of chamber60a.

The embodiment ofFIGS. 4aand 4balso show another option for orientation wherein slots are formed with their lengths extending more circumferentially, substantially orthogonal relative to axis x. For example, each slot62has a length that extends about a portion of the circumference of the side wall60d,while the width of the slot extends axially. This is different than the slots16ofFIGS. 1, 2 and 3b, which extend with their lengths oriented axially, substantially parallel to the long axis x.

The embodiment ofFIGS. 4aand 4boffers an adjustability to select for slot dimensions wherein the slot is formed by a radial flange66and an end plate67or second flange that is adjustably connected to the radial flange. The width W of the slots is determined by the proximity of end plate67to flange66and this proximity can be adjusted by fasteners68and/or spacers69. Spacers69can be configured, such as being pie-shaped, to each block a segment of the gap between flange66and end plate67and the open areas between the spacers are the slots. If it is desired to have a slot spanning substantially the full circumference of the side wall, the spacers can be eliminated or reduced significantly in size. In such an embodiment, the slot dimensions can be adjusted to simulate the fracture profiles regarding fracture width and orientation.

Flow through the fracture simulator is shown by arrows F. It will be appreciated, the slots remain on the side wall such that flow passing through the must be diverted perpendicularly to pass through slots in the same way that flow in a wellbore must change direction from axial flow to perpendicular flow to pass through wellbore fractures.

In the embodiment ofFIGS. 4a/4b,the fracture simulator also offers a slot characteristic with respect to slot depth D. As such, while the embodiments ofFIGS. 1 to 3bhave a slot depth limited by the thickness of sidewall14c,the slots62ofFIG. 4bhave an extended depth greater than the side wall thickness more similar to the wellbore fracture profile, in particular simulating partial fracture half depth. This fracture simulator construction offers selection based on the third dimension of depth. With such a construction, the depth of the bridge formed by any particular diversion material can be determined for any slot width, as may be useful for volumetric calculations related to field applications. In contrast, the embodiment shown inFIGS. 3a-3dtests the placement of a near wellbore diversion material seal. In particular, the diversion material is deposited on the sidewalls and in the slot, which has a minimal depth—only the thickness of the simulator wall.

One or both of the parallel surfaces of slots62formed by flange66and end plateFIGURE 67can have different tolerances and/or surface roughening to simulate downhole fracturing conditions such as rock properties, permit testing of back pressure effects. Alternately or in addition, the flange66and/or end plate may be made of clear material to permit visualization of the bridging and diverter activity as a performance result.

FIG. 4billustrates a diverter bridge69be formed in each slot62. Generally, larger diameter particles69abegin to catch in the gap forming slot62and then smaller diameter particles are forced by continued flow, arrows F, through slots62to pack in behind the larger particles.

If the test fails to achieve a seal in the slots, it may be determined that the diversion material is not appropriate for the slot profile and, therefore, the fracture profile. If the test does show a pressure increase, this is indicative of the formation of a seal in the slots, and it may be determined that the diversion material is appropriate for the slot profile and therefore the fracture profile.

Another fracture simulator70that includes a structure for simulating depth of penetration is shown inFIGS. 5a-5c. While simulator70has an axially extending slot72, it is similar to fracture simulator60in that it has a plate structure that extends the depth D of the slot. The plate structure includes a pair of plates74connected by solid walls73along the top and bottom and with a base end74aand an open outlet end74b.The plate structure, specifically base ends74aof the walls, are connected in a fluid tight manner against side wall70bof the fracture simulator encircling the slot and extend out therefrom a length to define depth D.

To simulate a fracture, the plate structure is an extension of at least the width dimension of the slot opening in side wall70b.In other words, space between the inner facing surfaces of walls74is no larger than the distance between side edges of the slot opening in wall70b.The space between facing inner surfaces of walls74defines width W. While width W may remain consistent along depth D, if desired, the width may taper to a narrower width W′ towards open outlet end74bas again may simulate certain wellbore fracture profiles. The width W of the slot can be selected and an apparatus may have more than one such fracture simulator, each one with a different slot W.

As noted above with respect to fracture simulator60, the inner facing surfaces74cof plates74may have surface roughness and/or the plates may be transparent to permit observation of the bridging action and the bridge79formed. In one embodiment, at least the inner facing surface of one or both plates are formed of the rock of the formation profile being tested.

Fracture simulator14ofFIG. 1also includes a structure, housing30, to simulate fracture depth. Housing30is installed exteriorly about the cylindrical outer wall of simulator14at least encircling the area axially outside of slot16. In the illustrated embodiment, housing30is installed on the inlet end of the fracture simulator or to the outlet end12b.Housing30may be releasably installed. The exterior housing30redirects fluid and diversion material passing out through the slot and creates some back pressure which can also be controlled depending on surface roughness and distance of the gap between housing30and slot16. While a fracture simulator without a housing requires a diversion material bridge to be formed at the side wall14d,a fracture simulator with exterior housing30permits the diverter bridge to form at a depth. Housing30offers simulation with respect to the third dimension of fracture geometry: depth D. Regardless, the exterior housing includes an open outlet therefrom to permit fluid to discharge from the exterior housing. In one embodiment, the exterior housing is a pipe with a diameter larger than the pipe with slot16and the pipe forming the exterior housing is sleeved over the pipe with a known distance gap between the slot and the inner wall of the exterior pipe. The fracture simulator may include an exterior housing installed outside the controlled slot size. The exterior housing contains the fluid and diversion material passing through the slot and creates some back pressure which can also be controlled depending on surface roughness and distance between housing and slot. Exterior housing can be used to represent the depth of penetration of the diverter bridge. This represents the third degree of fracture geometry, length of slot or depth. This exterior housing can also include a variable width slot which allows fluid to propagate through the slot.

As with each of the fracture simulators, the releasable connection15on fracture simulator14facilitates replacement of the fracture simulator, which has a known slot profile (i.e. width, depth, surface roughness, orientation) with another simulator that has a different slot profile. An apparatus may include a number of fracture simulators, each with similar releasable connectors but different slot flow area geometry and/or orientation. The releasable connection may be a quick release fitting, flange, threads, etc.

In the method, a diversion material can be selected to cause pressure diversion for a particular fracture profile and/or fracture fluid. Diversion material particle size, such as including particle size distribution can be selected for a particular fracture profile such as fracture width, length, depth, rock roughness, orientation. Other fracturing fluid factors can be tested, such as by addition of additives to the diversion material or the fracturing fluid type to test for pressure and/or flow rate response. Alternately or in addition, the method and apparatus can test the various new or modified diversion materials such as the effects of adding various diversion materials and/or additives on dissolution time. Alternately or in addition, the method and apparatus can test the effects of adding proppant into the diversion material. Alternately or in addition, the method and apparatus can test the effects of adding solid or liquid production chemicals into the diversion material.

A possible test procedure to validate a particular diversion material as suitable to create a pressure seal against a wellbore fracture in a formation includes the following steps:

1. Determine the fracture profile of the formation and select a fracture simulator to correlate to the fracture profile—may also consider wellbore conditions such as a temperature, hydrocarbons encountered and duration of diversion seal required;

2. Characterize a diversion material to be tested (i.e. select material alone, blends, particle size distributions, with or without additives such as proppants)—selected diversion materials tested and weighed;

3. Prepare diversion materials for launching—entrain diversion materials in a carrier fluid, gel hydrate, etc. and mix to achieve a selected concentration;

4. Prime the pump and flush piping to establish baseline pressure—this may be conducted through the direct line or before pill is loaded;

5. Prepare to launch the diversion material—shut down pump and load pill, release pill into flowing fluid or select valve to open the by-pass loop through the launching chamber;

6. Launch diversion material and monitor pressure—pump fluid to launch diversion pill while monitoring/recording pressure change;

7. Pressure bleed off and remove fracture simulator;

8. Inspect the bridge formed;

9. Collect diversion material from the fracture simulator;

10. Dry and weigh the collected diversion material; and

11. Repeat as desired to test different diversion materials, additives or fracture simulator options.

If the intent of the test is to assess a plurality of pills, the test may launch a plurality of pills into the fracture simulator prior to pressure bleed off and removal of the fracture simulator.

If the intent of the test is to validate a new diversion material (i.e. particle size, chemical composition or blend), the method may not require an assessment of the fracture profile of a formation, but rather may test the new diversion material against a range of slot dimensions to observe its performance results over a range of fracture simulators and thereby characterize its activity with respect to a range of simulated wellbore conditions.

If the intent of the test is to test solubilization rate of the diversion material, the fluid contact may be maintained in the fracture simulator for a selected residence time and a plurality of tests may be performed with different residence times.

A successful test result is shown inFIG. 6, wherein use of the apparatus ofFIG. 2with a Type 2 diversion material successfully showed pressure diversion (i.e., full or high % blockage) of a 2 mm slot in a fracture simulator. The pressure increased to 90 psi before the control system shut down the pump.