Abstract:
A method and apparatus for downhole coring while receiving logging-while-drilling tool data. The apparatus includes core collar and a retrievable core barrel. The retrievable core barrel receives core from a borehole which is sent to the surface for analysis via wireline and latching tool The core collar includes logging-while-drilling tools for the simultaneous measurement of formation properties during the core excavation process. Examples of logging-while-drilling tools include nuclear sensors, resistivity sensors, gamma ray sensors, and bit resistivity sensors. The disclosed method allows for precise core-log depth calibration and core orientation within a single borehole, and without at pipe trip, providing both time saving and unique scientific advantages.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a continuation of U.S. patent application Ser. No. 10/850,691, filed May 21, 2004, which claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 60/499,265, filed on Aug. 29, 2003, entitled SYSTEM FOR PERFORMING DOWNHOLE LOGGING WHILE CORING, both of which are expressly incorporated herein by reference in their entireties. 
     
    
     STATEMENT AS TO FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     The invention described herein was made at least in part with U.S. government support under Contract No. JSC 2-94, which was awarded by the U.S. National Science Foundation to Joint Ocean Institutions, Inc. and subcontracted to the assignee and under Contract No. JSC 2-06, which was awarded by the U.S. Department of Energy to Joint Ocean Institutions, Inc. and subcontracted to the assignee. Accordingly, the government may have certain rights in the subject invention. 
     
    
     BACKGROUND  
       [0003]     1. Technical Field  
         [0004]     The invention relates generally to a method and apparatus for wellbore coring and logging. More particularly, this invention relates to a method and apparatus for collecting data regarding geological properties of underground or undersea formations during coring operations.  
         [0005]     2. Discussion of Related Art  
         [0006]     The desirability of a system which is able to measure downhole formation properties while simultaneously coring a geological sample has long been recognized. Until now it has not been possible to continuously collect large diameter core and in situ logging data simultaneously.  
         [0007]     Geologists and geophysicists collect data regarding underground formations in order to predict the location of hydrocarbons (e.g., oil and gas). Traditionally, such information is gathered during an exploration phase. In recent years, however, the art has advanced to allow the collection of geophysical and geological data as a well is being drilled. These logging-while-drilling (LWD) measurements are typically made following coring in a separate borehole. Logging data are correlated to the core sample. Correlation accuracy depends on the yield recovery of the core and sample/data match-up. There is a pressing need in the industry for more accurate formation property data, such as provided by correlation of the core to a downhole data set.  
         [0008]     Known systems (e.g., logging-while-drilling) use a series of tubes, referred to as drill pipe and collars, to drill a hole into the formation. The lower end of the drill string, called the bottomhole assembly, is provided with a cutting mechanism, referred to as drill bit, which has a concentric hole. A drill collar, disposed proximally to the drill bit, includes several formation properties sensors, referred to as an LWD tool. Formation property measurements are recorded in this LWD tool.  
         [0009]     When a sample of the formation is required, a coring device is lowered inside the drill string and secured at the bottom end. By resuming drilling and/or pumping fluid down the drill string, the coring process is effected. The coring device is retrieved by a latching mechanism attached to a wireline.  
         [0010]     Continuous wireline-retrievable coring, for example, is routine in nearly all Ocean Drilling program (ODP) drill holes, whereas industry coring programs are often limited in key intervals due to time and cost constraints. The ODP routinely drills holes up to 2000 m deep without a riser in water depths ranging from 300 m to 6000 m. Sea water is utilized at high pressure to clear the hole of cuttings. Conventional wireline logging tools are typically deployed if hole conditions are good. In cases where drilling is expected to be difficult, LWD technologies are employed in another hole in close proximity to the core hole. A dedicated LWD hole is often the only alternative to collect in situ log data in such difficult drilling environments.  
         [0011]     In order to obtain logging-while-drilling data and a closely correlated core sample, the prior art requires two holes to be drilled. A first hole is drilled to collect a core sample. A coring bottomhole assembly is used to simultaneously drill a hole and core out a core column. A second hole, laterally spaced from the first hole, is drilled using a traditional logging-while-drilling bottomhole assembly. Logging-while-drilling tools measure formation properties of borehole that are, in theory, supposed to be closely correlated to the previously extracted core sample.  
         [0012]     The prior art exhibits two significant disadvantages. The above described method is time consuming because it requires two separate drill holes: a first hole for obtaining core samples and a second hole for obtaining logging-while-drilling data. Specifically, a downhole coring assembly must be lowered to the ocean floor, in order to drill/core the first hole. Subsequently, the downhole coring assembly is raised to the surface so that a retooling can be executed. A logging-while-drilling downhole assembly is then lowered back down to the ocean floor in the area of the first hole. Following the positioning of the logging-while-drilling downhole assembly, the assembly drills the second hole while performing logging-while-drilling measurements. The time required in refitting the drillstring with the logging-while-drilling assembly and in drill the second hole adds to the total operating costs and time duration of this coring and logging operation.  
         [0013]     The second disadvantage is the possible detrimental effect on the data correlation. Correlating a core sample with formation property data assumes that the data and sample are obtained from same location or even the same hole. When the logging data and core sample are obtained from different holes that are often located some distance from each other, one&#39;s ability to correlate the logging data with the core sample to obtain accurate result can be adversely affected.  
       SUMMARY OF THE INVENTION  
       [0014]     A new logging-while-coring technology is proposed. A primary object of the present invention is the reduction of time required to log after drilling and coring has been completed in a hole. Another object of the present invention is to make in situ measurements using LWD over the same cored interval in a particular hole. Merging state-of-the-art wireline coring and logging while drilling technologies provides two vital data sets without sacrificing time or adding risk associated with longer open hole times.  
         [0015]     The invention relates primarily to a downhole rotary coring device placeable in a drill string and having a head section, a drill collar, and a core barrel having LWD tools disposed within the drill collar. The coring device is used to obtain a sample of an earth formation. The invention provides a combined downhole coring device with a collar for performing LWD measurements.  
         [0016]     The coring device has a core barrel with a coring bit at the lower end, which cuts an annular hole into the formation. The resulting pillar of rock enters the core barrel and held in place by a core catcher.  
         [0017]     Formation property measurements are executed during the coring process. Formation property sensors are powered by an internal battery contained within the drill collar. Formation property data are stored in a memory storage device, such as, Random Access Memory (RAM), and/or communicated to a data transmission system.  
         [0018]     The purpose of the present invention is to propose a solution to the problem set out above. One object of the invention is to procure a collar that allows both a core barrel pass through it and is able to perform logging-while-drilling measurements.  
         [0019]     According to one aspect of the invention, a downhole assembly for performing logging operations while coring includes a core bit disposed at a distal end of the assembly and a core barrel having an inner surface and an outer surface. The core barrel is coupled to the core bit. The assembly further includes a collar having an inner surface and an outer surface and at least one logging sensor. The inner surface of the collar allows the outside surface of the core barrel to pass through it. At least one logging sensor is disposed on the outer surface of the collar.  
         [0020]     According to another aspect of the invention, the downhole assembly further includes logging-while-drilling tools.  
         [0021]     According to another aspect of the invention, the downhole assembly further includes a core catcher.  
         [0022]     According to another aspect of the invention, the downhole assembly further includes one or more crossovers.  
         [0023]     According to another aspect of the invention, the downhole assembly further includes one or more jarring devices.  
         [0024]     According to another aspect of the invention, the downhole assembly further includes one or more stabilizers.  
         [0025]     According to another aspect of the invention, the downhole assembly further includes a battery powering at least one of the logging sensors.  
         [0026]     According to another aspect of the invention, the battery is disposed within the collar.  
         [0027]     According to another aspect of the invention, the core barrel is powered by a motor, or another driving mechanism.  
         [0028]     According to another aspect of the invention, the downhole assembly is disposed in a drillstring.  
         [0029]     According to another aspect of the invention, the logging sensors measures formation properties of the surface of the wellbore.  
         [0030]     According to another aspect of the invention, the logging sensors includes one or more sensors from a group consisting of: resistivity sensor; passive nuclear sensor; active nuclear sensor; gamma ray sensor; electromagnetic wave sensor; electric field telemetry sensor; acoustics sensor; and nuclear magnetic resonance sensor.  
         [0031]     According to another aspect of the invention, the logging sensor communicates with a data transmission device.  
         [0032]     According to another aspect of the invention, logging data is stored in a memory storage device.  
         [0033]     According to another aspect of the invention, a method for executing logging measurement while performing coring operation is disclosed. The method includes providing a bottomhole assembly, coring a wellbore, and receiving measurements from one or more logging tools. At least one logging tool measures a formation property of a wellbore.  
         [0034]     According to another aspect of the invention, the method for executing logging measurement while performing coring operation further includes the step of communicating the measurements to a data transmission device.  
         [0035]     According to another aspect of the invention, the method for executing logging measurement while performing coring operation further includes the step of storing the measurements in a memory storage device.  
         [0036]     According to another aspect of the invention, the method for executing logging measurement while performing coring operation further includes the step of receiving measurements from a least one measurements-while-drilling tools.  
         [0037]     According to another aspect of the invention, the method for executing logging measurement while performing coring operation further includes the step of communicating the measurements from at least one measurements-while-drilling tools to a data transmission device.  
         [0038]     According to another aspect of the invention, the method for executing logging measurement while performing coring operation further includes the step of storing the measurements from at least one measurements-while-drilling tools in a memory storage device.  
         [0039]     According to another aspect of the invention, a method for performing logging operations while coring includes the steps of excavating a core sample, capturing the core sample through a core bit into a core barrel, and activating at least one logging sensor. Each of the logging sensors measures one or more formation properties. The method further includes the step of receiving sensor measurements from at least one logging sensor.  
         [0040]     According to another aspect of the invention, the method for performing logging operations while coring further includes the step of communicating the sensor measurements to a data transmission device.  
         [0041]     According to another aspect of the invention, the method for performing logging operations while coring further includes the step of storing the sensor measurements in a memory storage device. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0042]     In the drawing,  
         [0043]      FIG. 1  is a schematic of the prior art representing a logging-while-drilling downhole assembly;  
         [0044]      FIG. 2  is an illustration of a logging-while-coring downhole assembly;  
         [0045]      FIG. 3  is an illustration of an additional embodiment of a logging-while-coring downhole assembly with a retrievable memory module;  
         [0046]      FIG. 4  is an illustration of an additional embodiment of a logging-while-coring downhole assembly with a mud pulsing unit;  
         [0047]      FIG. 5A  is a representation of a location map of the Hydrate Ridge test site off the coast of Oregon;  
         [0048]      FIG. 5B  is a bathymetrical representation of the Hydrate Ridge test site off the coast of Oregon;  
         [0049]      FIG. 6  is an illustration of core recovered using the logging-while-coring system;  
         [0050]      FIG. 7  is a representation of data acquired from Site  1249 B including resistivity images, resistivity and gamma curves and data from core collected through the logging while coring system;  
         [0051]      FIG. 8  is a representation of data acquired using the GVR-6 and VDN tools from Hole  1249 A, adjacent to Hole  1249 B; and  
         [0052]      FIG. 9  is representation of a comparison of responses between the data acquired using the GVR-6 and VDN tools and logging-while-coring tools. 
     
    
     DETAILED DESCRIPTION  
       [0053]     The present invention combines a coring system with logging-while-drilling system, both of which are known in the art.  
         [0054]     A schematic of the prior art is depicted in  FIG. 1 .  FIG. 1  illustrates a logging-while-drilling downhole assembly  100 . The logging-while-drilling downhole assembly  100  includes a bit  110 , a bit sub  120 , a measurement-while-drilling section  130 , a logging-while-drilling lower sub-assembly  140 , a mechanically-rotatable-turbine section  150 , and a logging-while-drilling upper sub-assembly  160 .  
         [0055]     Bit  110  is comprised of three rotatable heads that break up rock when a force is applied to the logging-while-drilling downhole assembly  100 . Bit sub  120  is a pipe sub-assembly that couples the bit  110  to the rest of the logging-while-drilling downhole assembly  100 .  
         [0056]     Measurement-while-drilling (MWD) section  130  performs measurements such as sensing ambient pressure and weight on bit  110 . Logging-while-drilling lower assembly  140  performs logging measurements, such as, sensing shallow resistivity, medium resistivity, deep resistivity, ring resistivity, and gamma rays. Mechanically-rotatable-turbine  150  includes a hydraulic turbine motor, read out port magnets, and antennas.  
         [0057]     Logging-while-drilling upper assembly  160  performs logging measurements. Logging-while-drilling upper assembly  160  includes a far neutron sensor, a near neutron sensor, a neutron source. Logging-while-drilling upper assembly  160  further includes a long density sensor, a short density, a density source, and a ultrasonic sensor.  
         [0058]      FIG. 2  illustrates an embodiment of the present invention. Logging-while-coring downhole system  200  is disposed at the distal end of a drillstring (not shown) and is lowered into a wellbore to perform drilling, coring, and logging operations. Logging-while-coring downhole system  200  includes a core collar  210 , a retrievable core barrel  220 , a battery  230 , a ring resistivity electrode  270 , an azimuthal gamma ray detector  280 , a field replaceable stabilizer  290 , and bit resistivity electrode  295 . Logging-while-coring downhole system  200  further includes a shallow azimuthal resistivity electrode  240 , a medium azimuthal resistivity electrode  250 , and a deep azimuthal resistivity electrode  260 .  
         [0059]     The current embodiment of the present invention was reduced to practice by selecting a core barrel to fit through the throat of a modified Schlumberger Resistivity-at-Bit ™ (RAB-8™) Tool. A core barrel (MDCB)  220  was selected to fit within the 3.45-inch annulus of the RAB-8. Minor modifications of the MDCB  220  were required to accommodate the tool length and latching mechanism.  
         [0060]     A typical RAB-8 battery ordinarily occupies the annular space in the tool. The RAB-8 battery was redesigned to retain the annular space, allowing the MDCB  220  to pass through. A new resistivity button sleeve and slick stabilizer were fabricated to accommodate a 9⅞-inches bit size which is considerably smaller than conventional bits used with the RAB-8 collar. The tool standoff from the borehole wall for the core collar  210  is nominally 0.185-inches in the present configuration.  
         [0061]     Referring to  FIG. 2 , the logging tools are disposed within the core collar  210 . The battery  230  in the present embodiment powers the sensors ( 240 ,  270 ,  280 ,  295 , etc.) and any memory storage devices (not shown), such as RAM, EEPROM, flash, etc. However, in alternate embodiments, power can be supplied from the surface through a wireline (not shown).  
         [0062]     Retrievable MDCB  220  rotate circumferentially and is driven by a motor (not shown). Rock and sediment ingress into the hollow body of retrievable MDCB  220 . Upon extraction of core from the wellbore into the retrievable MDCB  220 , retrievable MDCB  220  is unlatched and brought to the surface via a tether (e.g., slickline). The retrievable MDCB  220  can be replaced in situ by running another core barrel down from the surface. Within the scope of the present invention, the core barrel is not limited to a retrievable motor driven core barrel  220 . Other embodiments can include piston-type core barrel, a static core barrel, or non-retrievable core barrel.  
         [0063]     Referring to  FIG. 2 , three azimuthal resistivity electrodes are illustrated. Shallow azimuthal resistivity electrode  240  senses the resistivity of the surrounding rock formation at a depth shallower relative to the other sensors. Medium azimuthal resistivity electrode  250  senses the resistivity of the surrounding rock formation at medium depth relative to the other sensors. Deep azimuthal resistivity electrode  240  senses the resistivity of the surrounding rock formation at a depth deeper relative to the other sensors. The resistivity sensors of the present embodiment functionally operate in similar manners. Resistivity of the surrounding formation is measured by applying a voltage to one or more electrodes and measuring the current passing through the electrode as a function of the voltage in accordance with Ohm&#39;s law. Ring resistivity electrode measures  270  performs a similar measurement using a ring-shaped electrode by measuring resistances of all azimuths around the borehole.  
         [0064]     Azimuthal gamma ray detector  280  senses gamma rays propagating through the formation of the wellbore. Gamma rays are produced by the nuclear decay of clays in the surrounding formation. Field replaceable stabilizer  290  maintains the collar  210  centralized and stabilizes the collar  210  in the hole. Field replaceable stabilizer  290  is also able to be changed on the surface. Bit resistivity electrode  295  measures the resistivity of the formation at the bit.  
         [0065]     Other embodiments may employ active nuclear sensors in the logging-while-coring system. For example, a neutron source for neutron bombardment and neutron detector may be used in the outer surface of the core collar. Another example includes a electron source for electron emission and electron detector may be used in the outer surface of the core collar.  
         [0066]      FIG. 3  illustrates an alternate embodiment of the present invention. Referring to  FIG. 3 , the logging-while-coring tool  300  includes a core barrel  330 , a logging-while-drilling tool  320 , a drill bit  340 , a core barrel retrievable memory module  350 , and an inductive coupler  370 . The core barrel  330  and the retrievable memory module  350  are coupled to one another.  
         [0067]     Logging-while-drilling tool  320  is similar in construction to the core collar  210  of the previous embodiment. Logging-while-drilling tool  320  includes drilling sensor sub assembly  310  and one or more logging tools (not shown) that are known in the art. Data from the logging tools (e.g., weight on bit, torque, and pressure) are communicated to the drilling sensor sub assembly  310 . The drilling sensor sub assembly  310  communicates the data through the inductive coupler  370 .  
         [0068]     The inductive coupler comprises an inner inductor  370  and outer inductor  380 . The inner inductor  370  and the outer inductor  380  are disposed in the core barrel retrievable memory module and the drilling sensor sub assembly  310 , respectively. The outer inductor  380  transmits the logging data via an induced magnetic field which is produced by current passing through the outer inductor  380  in accordance with Ampere&#39;s law. The resultant magnetic field induces a current in the inner inductor  370  in accordance with Faraday&#39;s law. A retrievable memory module (not shown) of the core barrel retrievable memory module  350  recognizes and stores the signal received from the inner inductor  370 .  
         [0069]     In one or more embodiments, the drilling sensor sub assembly  310  transmits the data via the inductive coupler  360  whether the core barrel retrievable memory module  350  is present or not. In some embodiments, the core barrel retrievable memory module  350  performs and stores its own measurements in addition to the logging data received from the drilling sensor sub assembly  310 . For example, the core barrel retrievable memory module  350  executes pressure and acceleration measurements which are stored with the data transmitted from the inductive coupler  360 .  
         [0070]     In the present embodiment, the retrievable memory module  350  includes a 64 MB flash memory chip. In other embodiments, the retrievable memory module can include one or more of a variety of memory-storage devices. Examples of memory storage devices include random access memory (RAM), electronically erasable programmable read only memory (EEPROM), and flash RAM.  
         [0071]     The memory storage device stores the data received from the LWD tools and is downloadable at the surface following a logging-while-coring operation. During retrieval of the core barrel  330 , the core barrel retrievable memory module  350  is also brought to the surface. The data corresponding to the sample contained in the core barrel is retrieved at the surface through a computer interface.  
         [0072]      FIG. 4  illustrates another embodiment of the present invention. Referring to  FIG. 4 , the logging-while-coring tool  400  includes a core barrel  430 , a logging-while-drilling tool  420 , a drill bit  440 , a core barrel retrievable memory module  450 , a full gauge washer  470 , a mud pulsing telemetry unit  480 , and an inductive coupler  470 . The core barrel  430  and the retrievable memory module  450  are coupled to one another.  
         [0073]     Logging-while-drilling tool  420  is similar in construction to the logging-while-drilling tool  320  of the previous embodiment. As such, logging-while-drilling tool  420  includes drilling sensor sub assembly  410  and one or more logging tools (not shown) that are known in the art. Data from the logging tools (e.g., weight on bit, torque, and pressure) are communicated to the drilling sensor sub assembly  410 . As in the previous embodiment, the drilling sensor sub assembly  410  communicates the data through the inductive coupler  470 . A retrievable memory module (not shown) of the core barrel retrievable memory module  350  recognizes and stores the signal received the inductive coupler  470 .  
         [0074]     Data received from the inductive coupler is also communicated to the mud pulsing telemetry unit  480 . The mud pulsing telemetry unit  480  includes a circuit and transducer that receives the downhole data signal and produces a highly correlated pressure signal. The mud pulsing telemetry unit telemeters the data up the drill string to the surface. The transducer produces pressure waves  490  that propagate through the mud contained in the interior of the drill string. The transmission of downhole data to the surface occurs in real time.  
         [0075]     The pressure waves  490  represent a binary signal that is decoded at the surface. In other embodiments of the present invention, the pressure waves  490  can represent an analog signal.  
         [0076]     This embodiment can also include a core barrel retrievable memory module  450  which receives and stores downhole logging data. The core barrel retrievable memory module  450  can also be used as to buffer the data signal before transmission to the surface via the mud pulsing telemetry unit  480 . The retrievable memory module contained therein can include one or more of a variety of memory storage devices. Examples of memory storage devices include random access memory (RAM), electronically erasable programmable read only memory (EEPROM), and flash RAM.  
         [0077]     As with the previous embodiment, the core barrel retrievable memory module  450  can be brought to the surface during the retrieval of the core barrel  430 . The data corresponding to the sample contained in the core barrel is retrieved at the surface through a computer interface.  
         [0078]     Following the reduction to practice of the logging-while-coring system, the logging-while coring system was tested. A coring test through low-grade cement was successfully conducted prior to deployment of the system at sea.  
         [0079]     Proof of concept ocean drilling test were performed during Ocean Drilling Program Leg  204  on Hydrate Ridge off the coast of Oregon. The logging-while-coring system was deployed on a vessel called D/V JOIDES Resolution for use on ODP Leg  204 , offshore Oregon, in July 2002. The test was conducted in 788.5 m water depth at the crest of southern Hydrate Ridge at ODP Site  1249  ( FIGS. 5A &amp; 5B ). Drilling proceeded to 30 m below sea floor where coring operations began with sequential 4.5-m, then 9-m-long cores recovered through gas hydrate-bearing clay sediments to 74.9 m depth. A 9⅞-inch-diameter four-cone bit (not shown) was used and the rotation rate increased from 15 to 45 RPM with depth. Average penetration rate was approximately 8 m/hr.  
         [0080]     Eight cores were recovered from Hole  1249 B with 32.9% recovery, on average, through a 45 m interval. Cores recovered using plastic liners have a slightly narrower diameter (2.35″) than more standard cores, yet recovery as high as 67.8% was reached. Two 9-m (2.56″ diameter) cores were taken without MDCB liners and achieved up to 42.3% recovery after being extruded from the barrel. Without liners, however, handling and further core processing and archiving is limited.  
         [0081]     All eight cores were processed and archived normally on board the D/V JOIDES Resolution.  FIG. 6  illustrates the first core recovered from Hole  1249 B prior to measurement and processing. Core measurements including density and magnetic susceptibility were made onboard the JOIDES Resolution using a multi-sensor track. Bulk density, porosity and grain density core measurements were made on discrete samples. The occurrence of gas hydrates in the core material and their rapid dissociation precluded the measurement of natural gamma activity in the cores. These measurements require an extended length of time to complete the measurement process.  
         [0082]     High quality logs and image data were recorded in the downhole memory of the logging-while-coring tool over the entire 74.9 m drilled interval in Hole  1249 B. The RAB-8 system was also calibrated post-deployment in salt water calibration tanks at Sugar Land, Tex. The tool functioned properly during this test and the calibration showed the field data are reliable.  
         [0083]      FIG. 7  shows a summary of the primary core and drilling data acquired in Hole  1249 B including resistivity images, and the resistivity and gamma ray logs from the logging-while-coring system. Core measurements of discrete samples from Hole  1249 B are presented at discrete depths from 29.9-75.0 m below seafloor (mbsf) as well as multi-sensor track core measurements. Core measurements have a depth accuracy of ±0.5 meters. Since core recovery averages only 32.9% in this hole, depth matching between core and log measurements may be somewhat imprecise at specific depths. Ties are made using density, magnetic susceptibility and gamma ray data, and for example, all three measurements increase near 60 mbsf, indicating a change in lithologic content.  
         [0084]     Downhole drilling parameters recording during coring in Hole  1249 B are also indicated in  FIG. 7 . Hole  1249 B was drilled to maintain a rate of penetration of 20 m/hr over each cored interval. Weight-on-bit ranged widely, however, as it was difficult to control precisely in these shallow and soft sediments. The time after bit (of the LWD system measurements) varies due to the time required to drill and recover each core, and substantially more time than standard drilling or LWD operations without coring is required. The difference between drilling ahead and coring time may introduce some uncertainly in the core to log depth correlation.  
         [0085]     Core photographs of core  5 -A (43 mbsf) indicates a gas hydrate rich core that largely dissociated creating a “mousse”-like fabric. The reflective areas are an indication of where the gas hydrate existed. Core  6 -A (49 mbsf) indicates a change in the composition of the cored material. The mixed recovery in these materials is reasonable given that the MDCB core barrel  220  is designed primarily for use in harder rocks. The MDCB system cuts core by rotation, filling of the barrel slowly as the bit advances. A piston-type core barrel is more conducive to high recovery of low-strength materials. The MDCB core barrel  220  will be modified in the future to shorten the core length and reduce friction as the core enters the barrel. These are important changes aimed at improving core recovery with this system.  
         [0086]     A comprehensive suite of LWD data was acquired in nearby Hole  1249 A using GeoVision Resistivity (GVR-6) TM and Vision Density Neutron (VDN) TM tools ( FIG. 8 ) which are known in the art. The lateral offset between Hole  1249 A and  1249 B is 40 m. A difference of approximately 0.5 meters in water depth exists between the two sites. The logs from Hole  1249 A show the rate of penetration and time after bit curves are lower than in Hole  1249 B and remain relatively constant for the drilled interval ( FIG. 8 ).  
         [0087]     The logging-while-coring data collected in Hole  1249 B are compared with GVR-6 data from nearby Hole  1249 A in  FIG. 9 , which shows important similarities and differences. The large increase in resistivity in the upper interval in both holes corresponds to the presence of gas and gas hydrate. Some variation in the image quality between the holes may be associated with the greater time after bit for the logging-While-coring system measurements (e.g. coring versus drilling operations). The gamma ray shows a linear trend with an offset that may be attributed to the difference in lateral standoff between logging-while-coring and GVR-6 tools. In general, the image data in Hole  1249 A and  1249 B correlate well, with differences due to environmental conditions and lateral variations in geologic heterogeneity between the two sites.  
         [0088]     The deployment of a new logging-while-coring system on Hydrate Ridge successfully acquired resistivity and gamma ray logs, and resistivity image simultaneously with core in Hole  1249 B. This system offers the significant advantages of providing core and log data over the same drilled interval, and saving rig time. Time requirements for the logging while coring system are the same as for coring operations alone. Core recovery during this test reached 68.9% and averaged 32.8% over a 45 m drilled interval in shallow, soft marine sediments. Alternate deployments of the logging-while-coring system in harder rock environments offer the potential for improved core recovery using a motor driven core barrel. Core recovery in soft sediments may be increased by modifying other core barrels to fit within the 3.45 inch annulus of the core collar  210 . Measurements on recovered core may be correlated directly with log data over the same drilled interval. LWD data from both conventional and while-coring operations at a nearby site agree well, and indicate the presence of gas and gas hydrate in clay rich sediments at this location.  
         [0089]     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of the equivalency of the claims are therefore intended to be embraced therein.