Improved Techniques for Acquiring Pressure and Fluid Data in a Challenging Offshore Carbonate Environment

Contreiras, Kilamba Diogo; Van-Duinem, F.; Weinheber, Peter; Gisolf, Adriaan; Rueda, Marco Antonio

doi:10.2118/115504-ms

Cited by 2 publications

(1 citation statement)

References 8 publications

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“…Pumpout Module. A full discussion on formation testing pumps is available in Contreiras et al (2008), Weinheber et al (2008), andJackson et al (2009). During IPTT operations the pumpout module's primary purpose is pumping fluid from the interval through the tool flowline and into the wellbore.…”

Section: Introductionmentioning

confidence: 99%

Extending the Limit: Interval Pressure Transient Testing in Low-Permeability Reservoirs in the North Sea

et al. 2009

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The use of wireline-conveyed formation testers for sampling, downhole fluid analysis (DFA), interval pressure transient testing (IPTT), and producibility estimation is well established in the oil and gas industry. The increasing demand for hydrocarbons is driving the exploration and production of reservoirs previously deemed uneconomical. The low-permeability limit for such reservoirs is continually being reduced while the limit for reservoir temperature is increasing. IPTT techniques address these trends by extending the limits for high-quality data acquisition.The decision on whether to perform IPTT requires an estimate of permeability. This estimate usually comes from either pretesting or other well data such as nuclear magnetic resonance (NMR) logs. However, these measurements have a shallow depth of investigation and may underestimate the mobility of the reservoir fluids because of formation damage such as fines invasion, or high-viscosity fluid in the invaded zone. To displace invaded fluids in low-permeability formations can be challenging, usually requiring a high drawdown to pump the mud filtrate and fines from the formation. High-performance packers and pumps are essential in such environments that require a large number of high differential-pressure cycles.In this paper three case studies of IPTT in low-permeability reservoirs in the North Sea are presented. In the first, pretesting with a single probe and dual-packer indicated a tight formation (no fluid communication between the tool and formation was established). IPTT was attempted and fluid moved at a drawdown of around 80 bar. The subsequent influx of formation gas reduced the drawdown significantly and a large increase in mobility was observed.In the second tight gas case study gas influx was detected, but because of the large drawdown the gas compressibility prevented a large-volume cleanup and the test was aborted. This case shows the limit of what is achievable in this environment.The third case study illustrates a very low-permeability limestone that was straddled with a dual-packer-standard-probe testing configuration. The downhole pump was equipped with a high-pressure displacement unit (DU). This pump configuration handled the high initial drawdown required to clean up the damaged zone. Initial cleanup pumping was followed by 30 hours of producing time and then a final pressure buildup. The result was a high-quality estimate of deep formation properties and fluid samples with very low contamination levels. A lesson learned was that formations considered "tight" according to data available before formation testing may be productive and capable of flowing hydrocarbons when evaluated with IPTT. Compared with the cost of a drillstem test (DST) in low permeability conditions, the dual-packer tool provided a fast, cost-efficient, and flexible way of testing individual zones. IntroductionFormation testing as the first direct trial of reservoir performance and producibility is extremely important. During a test important information for future fi...

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Section: Introductionmentioning

confidence: 99%

Extending the Limit: Interval Pressure Transient Testing in Low-Permeability Reservoirs in the North Sea

et al. 2009

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Equation-of-State-Based Downhole Fluid Characterization

et al. 2010

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Downhole fluid analysis (DFA), together with focused-sampling techniques and wireline-formation-tester (WFT) tools, provides real-time measurements of reservoir-fluid properties such as the compositions of four or five hydrocarbon components/groups and gas/oil ratio (GOR). With the introduction of a new generation of DFA tools that analyze fluids at downhole conditions, the accuracy and reliability of the DFA measurements are improved significantly. Furthermore, downhole measurements of live-fluid densities are integrated into the new tools. Direct pressure and temperature measurements of the flowline ensure capture of accurate fluid conditions. To enhance these advanced features further, a new method of downhole fluid characterization based on the equationof-state (EOS) approach is proposed in this work.The motivation for this work is to develop a new approach to maximize the value of DFA data, perform quality assurance or quality control of DFA data, and establish a fluid model for DFA log predictions along with DFA fluid profiling. The basic inputs from DFA measurements are weight percentages of CO 2 , C 1 , C 2 , C 3 -C 5, and C 6+ , along with live-fluid density and viscosity. A new method was developed in this work to delump and characterize the DFA measurements of C 3 -C 5 (or C 2 -C 5 ) and C 6+ into full-length compositional data. The full-length compositional data predicted by the new method were compared with the laboratory-measured gas chromatograph data up to C 30+ for more than 1,000 fluids, including heavy oil, conventional black oil, volatile oil, rich gas condensate, lean gas condensate, and wet gas. These fluids have a GOR range of 8-140,000 scf/STB and a gravity range from 9 to 50°API. A good agreement was achieved between the delumped and gas-chromatograph compositions.In addition, on the basis of the delumped and characterized full-length compositional data, EOS models were established that can be applied to predict fluid-phase behavior and physical properties by virtue of DFA data as inputs. The EOS predictions were validated and compared with the laboratory-measured pressure/volume/temperature (PVT) properties for more than 1,000 fluids. The GOR, formation-volume factor, density, and viscosity predictions were in good agreement with the laboratory measurements. The established EOS model then was able to predict other PVT properties, and the results were compared with the laboratory measurements in good agreement.Consequently, the established EOS models have laid a solid foundation for DFA log predictions in DFA fluid profiling, which has been integrated successfully with DFA measurements in real time to delineate compositional and asphaltene gradients in oil columns and to determine reservoir connectivity. The latter results are beyond the scope of this work and have been given in separate technical papers.

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Improved Techniques for Acquiring Pressure and Fluid Data in a Challenging Offshore Carbonate Environment

Cited by 2 publications

References 8 publications

Extending the Limit: Interval Pressure Transient Testing in Low-Permeability Reservoirs in the North Sea

Extending the Limit: Interval Pressure Transient Testing in Low-Permeability Reservoirs in the North Sea

Equation-of-State-Based Downhole Fluid Characterization

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