Offshore

Innovative Solutions for Offshore Core Handling

Weatherford Laboratories is an industry leader in deepwater core retrieval offering innovative technology for handling, stabilization, and preservation.

Our offshore workflow begins with understanding and meeting our client’s objectives for taking a conventional core. To enhance the accuracy of fluid saturation measurements, Weatherford’s wellsite team can dispense mud tracers into the mud system to quantify fluid invasion levels in the laboratory. Onsite plugging using non-contaminating cutting fluids for obtaining high level Sw and Rw results can be performed inside our DNV certified onsite buildings.

From the moment the core comes out of the ground, we regard safety as a key component during the handling/lifting phase of the operation. Weatherford Laboratories has a small footprint, pneumatic mechanical arm known as the RocKlaw™ for managing heavy core tubes throughout wellsite core processing.

Maintaining core integrity is essential to a successful coring operation. We provide several techniques for stabilizing the core, including: epoxy and foam stabilization of friable lithologies, Teflon shims for competent intervals, and dry ice freezing an unconsolidated core. Transporting stabilized core intervals to the shorebase in our advanced GPS, climate-controlled/shock-monitored core transport boxes further ensures that all core material is tracked and cared for as it is transported to the laboratory.

Our RockKlaw mechanical core handling device ensures safe, efficient, and fast movement of core samples from racking to transportation.
Weatherford Laboratories is an industry leader in petrophysical laboratory analyses, which are critically important to deepwater exploration, appraisal, and development.

The Importance of Petrophysical Evaluation in Offshore Reservoirs

Our analyses provide a better understanding of the basic rock properties, log calibration inputs to improve core-log calibration, and key parameters for advanced log interpretation.  Log calibration measurements such as electrical properties (m&n) and nuclear magnetic resonance (NMR) rely heavily on knowing the mineralogy prior to outlining a laboratory protocol. We routinely conduct these log calibration inputs using state-of-the-art benchtop equipment.

Electrical measurements are ideally designed to relate a reservoir rock’s porosity, brine, and hydrocarbon saturations to its in situ electrical conductivity. The advantages are to better understand and calculate oil and gas reserves, in addition to interpreting electrical resistivity logs related to the overall assessment of oil and gas in place.

NMR tests not only provide useful core analysis data, deduced from the fluid within the pores, but they also enhance data interpretation of NMR results from logging-while-drilling (LWD) tools. The core-based NMR studies provide an array of useful information, including: (1) determination of reservoir thickness and net pay; (2) verification of the formation’s liquid-filled porosity and log response; (3) calculation of a formation-specific permeability relationship; (4) determination of formation-specific parameters to determine BVI (irreducible) from the downhole tool; (5) determination of movable fluids from log responses.

NMR

The Importance of Geologic Services in Offhsore Reservoirs

Core imaging techniques have evolved to the highest level in the past couple years for characterizing conventional cores.

Dual-Energy CT Scanning is currently used to investigate the integrity of the core, structural dip, bedding features, bulk density values, mineralogy, and the overall level of heterogeneity present. CT scanning has become an essential first-order rock typing tool prior to extruding and/or slabbing cores (these methods rely on customized software and petrophysical mineral models). Subsequently; Weatherford Laboratories strategically performs sample selection from these images with the help of our petrophysical modeling software.

In most cases, our seasoned geological staff will recommend a suite of samples for a complete petrographic workup. Weatherford Laboratories petrographers have in-depth expertise in conducting thin section petrographic analysis (including digital mosaics) to directly identify grain types and sizes, matrix, cement types and porosity types. Thin section analysis ultimately provides accurate information about rock types, depositional environment, and diagenesis of the reservoir for both crystalline and non-crystalline (amorphous) materials.

Both thin section petrography and x-ray diffraction (XRD) are supplemented with scanning electron microscopy (SEM) to recognize the location of potentially damaging clays and other mineral components. When integrated with other mineralogical data, SEM allows for evaluation of formation damage and design of remedial treatments. In addition, SEM helps identify log interpretation problems such as low-resistivity pay intervals.

Weatherford Laboratories employs the latest in CT scanning technology to inspect, characterize, and document an entire cored interval with greater precision.

Wellbore Stability and Pore Pressure Drawdown Effects on Offshore Reservoirs

Failure to properly measure rock mechanic properties can cause a number of wellbore problems such as borehole instability, casing shear, subsidence, stuck pipe, and sand control issues. Together, these issues are estimated to costs the E&P industry billions of dollars each year in the form of lost or deferred production, expensive remediation, and intervention operations.

Weatherford's rock mechanics laboratory is able to conduct triaxial compressive strength tests on cylindrical core samples to understand how the rock responds to compressional stress. We also perform the unconfined compression test. Combined, this information helps determine the compressive strength, failure envelope, Poisson’s ratio, and Young’s modulus. In determining the Mohr-Coulomb failure envelope, three to four triaxial tests on samples recovered from the same depth are recommended to obtain trustworthy results.

In laboratory analyses for deepwater plays, we simulate the impact on the formation as the field produces and undergoes pore pressure drawdown. These are commonly referred to as uniaxial strain pore volume compressibility measurements. We measure core samples for bulk compressibility (the relative change in bulk volume due to unit change in applied stress) and pore volume compressibility (representing the relative change in pore volume). To measure the representative in situ compressibility of the core under reservoir production conditions, we conduct drawdown tests under both uniaxial strain and constant axial stress conditions. This test can also be conducted using an overburden ramping method by increasing axial stress while maintaining uniaxial stress condition.

Weatherford Labs has the experience and analytical tools to understand a core's rock mechanics and how these translate to better well construction decisions in the field.
Predicting reservoir performance requires a firm understanding of petrophysical properties, including: lithology, porosity, permeability, water saturation, and reservoir thickness.

Use of Special Core Analysis Inputs into Reservoir Simulations

At Weatherford Laboratories, we have the full range of capabilities to provide the necessary inputs for your reservoir simulation. Both capillary pressure and relative permeability play a critical role in tuning the reservoir model.

Capillary pressure is a key parameter in determining distribution of fluids in the reservoir. Several methods for measuring capillary pressure are available and carefully selected depending on timing requirements and rock type. These methods range from mercury capillary pressure (MICP) to ultra-centrifuge, and for extended-length testing, the porous plate method is utilized.

Reservoir producibility is controlled by several factors, one of which is relative permeability. With multiphase flow in porous media, relative permeability is a dimensionless measure of effective permeability of that particular fluid phase. Weatherford Laboratories employs a full complement of both steady-state and unsteady-state methods to measure relative permeability.

Dynamic flow techniques such as these are frequently used during our deepwater assessments to assist our clients with ground truth reservoir model inputs and help with field production projections. How these measurements play out depend largely on the wettability of the formation. Wettability plays a key role in understanding basic reservoir properties like relative permeability, capillary pressure, and resistivity. Weatherford Laboratories employs a range of lab methods, including Amott, Modified Amott/USBM, and contact angle measurements to measure the wettability of the rock formation in the presence of different reservoir fluids.

The Geochemistry Toolkit for Offshore Exploration

Oil geochemistry plays a critical role in all modern petroleum exploration programs in the Gulf of Mexico.  Routine applications of oil geochemistry in this and other deepwater plays include:

  • Assessing charge risk prior to drilling (using oil geochemistry and basin modeling)
  • Identifying pay zones in new wells (e.g., using geochemical mud gas logging)
  • Characterizing the petroleum systems responsible for an oil show or discovery (using biomarker analyses of shows or produced oils)
  • Determining reservoir compartmentalization
  • Identifying completion problems in wells

Although oil geochemistry and gas geochemistry can be used to solve a variety of Gulf of Mexico exploration and development problems, such projects require access to oil, rock, and/or gas samples. However, a company which needs these data may not have all the samples "in house" required to conduct a project. Fortunately, Over 3,900 Gulf of Mexico produced oil, seep oil, and piston core samples are available for analysis in various oil collections that can be searched using the online OilTracers Oil Library. This database can lead you to the samples needed to make a project feasible. For many of the samples, data have already been acquired by the laboratories that own the samples, which are available for purchase.

Chromatography reveals details of the reservoir like no other tool.

PVT and Flow Assurance in Offshore Reservoirs

The key data obtained from pressure-volume-temperature (PVT) reports include the following:

  • an understanding of fluid composition, density, viscosity, and compressibility;
  • gas in solution;
  • saturation pressure (bubble point and dew point);
  • flow assurance properties.

In offshore environments, Weatherford Laboratories frequently works with conventional oils, volatile oil, gas condensate, and dry gas.

Production and hydrocarbon transport costs are expensive and require a very clear understanding of how oils will behave when mobilized from their virgin, untapped formations. Flow assurance testing is required to ensure that economical flow of hydrocarbons will occur from the reservoir to the point of sale. Threats to flow assurance include a diverse set of components in the fluid which, under the right conditions of temperature and pressure, may deposit on the internal walls of the piping and process equipment to slow or ultimately stop flow.

Weatherford Laboratories’ suite of reservoir fluid analysis techniques is designed to identify the various components of the reservoir fluid that threaten flow assurance. We work with our clients to understand the specific flow assurance problems they want to solve. From there, we tailor a customized workflow assurance test protocol to address their challenges. In addition, we are prepared to detect and identify natural gas hydrate potential, which is a pervasive problem in deep and ultra-deep water fields that can quickly plug off a pipeline or riser if left untreated.

Weatherford Laboratories PVT analysis guides decisions on the best production scenarios for the long-term viability of the well.
Understanding the fundamentals of the formation rate sensitivities and grain size distributions is crucial in wellbore preparation planning prior to the initial completion phase of an Offshore play.

Fines Migration Issues in Unconsolidated and Friable Lithologies/Rock-Fluid Sensitivities in Offshore Reservoirs

Maintaining consistent production and prevention of formation damage can be a delicate balance.

E&P processes may cause formation damage if they reduce the natural inherent productivity of the formation or reduce injectivity of a water or gas injection well. Formation damage can take place at all stages of a well’s life, from drilling on through to its production decline. Our formation damage studies are custom tailored to identify a problem and offer the appropriate solution that will allow the well to be drilled, completed, and produced in the safest and most efficient manner possible.

Weatherford Laboratories deploys a wide range of formation damage laboratory test methods which are pertinent to deepwater completions that go beyond fines migration issues. Regardless of the play type, rock/fluid compatibility warrants a close-up understanding. Simplified benchtop testing such as capillary suction time (CST), or something more sophisticated like regained permeability measurements, can be used. In addition to either of these tests, we recommend that fluid-fluid compatibility be conducted to understand any scale tendencies and determine any rate sensitivities present in the formation.

Fines migration problems are recognized during the critical velocity/rate sensitivity tests, which are core flow tests conducted at various flow rates to determine at which velocity certain clay minerals may become dislodged and reduce permeability.