Downhole Fluid Analysis—The Missing Link


Modern wireline formation testers deliver a wide range of downhole rock and fluid properties at in situ reservoir con- ditions. Operators are running increasingly complex logging strings to obtain more and more information under ever more challenging conditions. A principal objective of for- mation testing is accurate fluid characterization. Misinter- pretation of reservoir fluid properties may result in nonop- timal well placement, completion strategy and facilities design as well as large errors in predictions of reserves, drainage volume and reservoir performance. There is little wonder that downhole fluid analysis (DFA) is now firmly entrenched in fluid characterization protocols. Blind sampling—without DFA—leads to under- or over- sampling of the reservoir fluids. Acquiring a single sample of the oil makes as little sense as acquiring a single sample of the rock. DFA provides the missing link for tying other fluid information—such as mud-gas data, geochemistry and pressure-gradient data—to laboratory measurements. The prohibitive cost and complexity of intervention in deepwater developments have made accurate fluid charac- terization essential. Topside and seafloor facilities must be in place prior to production, and any retroactive redesign of facilities can be inordinately expensive. Flow assurance, the first major technical hurdle encountered in deep water, was responsible for the prevalent use and increased accep- tance of wireline sampling throughout the last two decades. DFA played a pivotal role in enabling the fluid sampling needed in deepwater wells. The focus on flow assurance has now abated as operators have discovered a means to anticipate and mitigate this problem. Instead, the empha- sis has shifted to reservoir compartmentalization, for which DFA has also proved its value.


The early recognition of compartmentalization is a pri- mary driver for the use of DFA even in reservoirs outside the deepwater arena. Many of the giant Middle East car- bonate fields, discovered decades ago, still produce hydro- carbons. Nevertheless, because of reservoir heterogeneity and the limited utility of classical measurements such as resistivity and pressure gradients, important attributes including fluid contacts, oil-water transition zones and reservoir connectivity remain poorly understood. The situa- tion becomes more serious as water production increases, oil is bypassed and more wells must be drilled in transition or water-swept zones. DFA in open or cased hole is a power- ful tool for addressing such important unknowns in all kinds of reservoirs—not just those in deep water. Looking forward, the industry faces several essential tasks. It must develop advanced DFA sensors based on new physics and nanoscale technologies and optimize and minia- turize the design of existing ones. It must also expand DFA to other platforms such as LWD, coiled tubing, production


logging tools and permanent monitoring strings. Another challenge is to improve current answer products and inter- pretation workflows. Integration is also key. Fluid characterization based on a single technique or technology, such as mud-gas logs, pres- sure data from formation testing, PVT characteristics or wellsite fluid-chemistry analysis, is standard practice for most E&P operators. Integrated approaches involving mul- tiple tools and technologies are relatively uncommon. For accurate fluid and reservoir characterization, however, data from seismic surveys, well logs and formation testing must be integrated with information from other sources such as geochemistry and mud-gas logs. The proper geological con- text must also be considered. When these sources are sys- tematically combined through the missing link—DFA—the synergy delivers a highly accurate and robust picture of the fluids and the reservoir (see “Downhole Fluids Laboratory,” page 38). Shell’s Fluid Evaluation and Sampling Technologies (FEAST) global center of expertise routinely implements integrated approaches for fluid characterization. For exam- ple, advanced mud-gas logging data can be used for predict- ing fluid facies and picking sampling points for formation testing; PVT data can be calibrated against mud logging data; and DFA can provide fluid-property measurements in real time, during or in lieu of sampling. Integration ensures that evaluation objectives are addressed using optimal technologies and workflows. It improves operational deci- sion making and maximizes the value of information. Such integration is achievable only through a team effort involv- ing service companies and operators—one that is based on both parties knowing their respective roles and responsibil- ities and respecting each other’s perspectives and business needs. This is the collaborative working model that FEAST advocates, and DFA is at the heart of it.


Hani Elshahawi Manager, Fluid Evaluation and Sampling Technologies Shell International E&P Inc. Houston, Texas, USA


Hani Elshahawi leads Shell’s FEAST global center of expertise, which is responsible for the planning, execution and analysis of global high-profile formation testing and fluid sampling operations. Hani has more than 20 years of experience in the oil industry and has worked in both service and operating companies in more than 10 countries in Africa, Asia and North America. He has held positions in interpretation, consulting, operations, marketing and product development. The holder of several patents and author of more than 70 papers in petroleum engineering and the geosciences, he is currently the President of the SPWLA and a Distinguished Lecturer for the SPE.


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