Drilling Technology

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The well trajectory window plots planned and actual well trajectories on top of the formation cross section determined by the geosteering process. The formation layers are referenced to true vertical depth from offset well profiles. The cross-sectional view of the geological layers graphically display wellbore position with respect to reservoir boundaries.

The GeoSteering Screen eliminates expenditures wasted on directional wells which successfully follow a geometric plan but miss the intended target. Steering the drill bit according to downhole measurements allows the well path to follow the pay zone through changing horizons thereby maximizing production and increasing profits.

Commitment to service, quality and state-of-the-art technology allow

Schlumberger to be the dominant provider of drilling services in the deepwater environment.

Deepwater Drilling Services

Deepwater drilling is a dynamic term used to define drilling of hydrocarbon reserves in water depths which exceed accepted technology. Beyond water depths of 3000 ft, traditional offshore technology and methods do not meet the challenges of deepwater issues. Improved methodology, which utilizes proven equipment, must be combined with technological advancements to produce reserves in an economical manner in the deepwater environment.

The environment introduces unique problems, which challenge drilling methods both technically and economically. The primary problems stem from temperature effects and decreased overburden pressure. These result from the lack of formation above the mud line. Temperature effects alter mud rheology, which directly impacts well control. The formations often involve over-pressured zones comprised of unconsolidated sands. With increasing water depth, the fracture gradient decreases. This narrows the window in which the mud and drilling programs must operate to maintain well control.

Schlumberger Drilling Services is the dominant provider of drilling services to deepwater clients as a result of its commit ment to service quality and state-of-the-art technology. The proper usage of advanced and existing technology allows operators to safely and efficiently drill deepwater targets while reducing costly rig expenditures. The following information highlights some of the capabilities of Schlumberger in deep-water environments.

MWD Data Transmission

Recent enhancements to the Schlumberger MWD PowerPulse telemetry system have enabled the MWD signal strength to be more than tripled while at the same time doubling data transmission rates. To date, 9 out of 10 of the deepest wells in the world were drilled using the PowerPulse MWD system.

Pressure Measurements

Unconsolidated sediments are typical in deepwater formations and contain narrow windows between pore pressure and fracture gradient. Keeping the equivalent circulating densities (ECD) within the pressure window is a constant struggle. Failure to do so results in lost circulation or an influx of reservoir fluid. Water influxes near the mud line are detrimental because of the associated washouts. These washouts pro-

4s water depth increases, the difference between fracture pressure and formation pressure decreases; thus reducing Well Control" href="/well-control-2/kick-tolerance.html">kick tolerance and requiring exact measurements of downhole pressure.

4s water depth increases, the difference between fracture pressure and formation pressure decreases; thus reducing kick tolerance and requiring exact measurements of downhole pressure.

duce caverns in the wellbore, which can undermine the casing support structure or even eliminate the possibility of regaining well control.

APWD Annular Pressure While Drilling sensors monitor ECDs to ensure the mud program is contained within the allowable operating margins. Pressure sensors identify shallow water flows, formation kicks and cuttings buildup in the annulus before they become detrimental. Pressure data is also used to establish proper fracture gradients for well construction purposes. Pressure sensors are available on both VISION and CDR* Compensated Dual Resistivity tools.

Caliper Measurements

Caliper tools are available to monitor wellbore conditions. A primary usage of caliper data is the detection of flowing water sands near the seafloor. As the water flows into the wellbore, severe washouts can occur due to the low sand strength of the formation. Real-time calipers identify the volume of material required to cement such sands. A number of calipers are available on the various MWD/LWD tools including acoustic, resistivity and nuclear measurements.

Temperature Measurements

Temperature measurements are commonly used for diagnosing problems in production logging applications. These principles are be used to aid in the drilling of deepwater wells with MWD/LWD tools.

Under ground blowouts are common in deepwater where gas or liquid migrates to the seafloor in the casing annulus. LWD temperature data provides a means to identify unwanted flow which can be remedied by squeeze cementing the sand. After cementing the sand, temperature sensors are run on pipe to estimate the top of cement behind casing.

Temperature data, used in conjunction with pressure data, distinguish the difference between flowing sands and excessive build up of annular cuttings. Each produces an

Shallow water flow identified by annular pressure increases as measured by the APWD sensor.

increase in downhole pressure relating to an ECD problem. It is important to determine the root cause of the ECD problems since each will require different remedial action. The two problems are distinguished by an increase in annular temperature which is present in the case of formation fluid influx.

LWD Inductive Coupling

The LINC* tool provides a means to download LWD data should the bottom hole assembly become stuck. The captured formation evaluation data provides valuable information to aid in decision making in those circumstances. Additionally, the LINC tool has proven itself valuable in well construction by providing a means to obtain an accurate Leak-Off Test (LOT).

Fracture gradients are obtained by estimating downhole pressure buildup from stand-pipe pressure during a LOT. In deepwater wells, compressibility and thermal effects skew the downhole pressure estimation. The ambiguity involved does not allow the accuracy required in deepwater drilling because of the narrow wellbore stability margins. Differences of a few tenths of a lbf/gal can make the difference between one or two extra casing string requirements. An accurate fracture pressure is obtained by monitoring the actual downhole pressure while performing the LOT.

LINC provides the real-time connection to the LWD tool. LOT procedures demand very low pump rates to avoid fracturing the formation. These low pump rates are not sufficient to power the MWD tool for data transmission. With LINC, instantaneous changes in the downhole pressure buildup are detected which allow the test tube stopped before formation damage occurs.

Formation Evaluation Measurements

High quality LWD data augments wireline services to provide logging profiles which capture the required data while minimizing costs. A key feature is density and resistivity imaging capabilities to identify fractures and formation breakouts while drilling. Additionally, real-time data is available at surface and can be transmitted directly to the clients' office for immediate interpretation.

Schlumberger is committed to meeting the demands of the future. A deepwater center of excellence has been established to identify and develop cost effective, solutions to deep-water challenges. The center is focused on integrated solutions encompassing all aspects from the planning to completion of deep-water wells around the world.

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