Pressure Transient Analysis in Horizontal Wells in Some Sole Pit Area Fields, U.K.
- C.J. Gilbert (Shell U.K. Exploration and Production)
- Document ID
- Society of Petroleum Engineers
- SPE Reservoir Engineering
- Publication Date
- May 1996
- Document Type
- Journal Paper
- 101 - 108
- 1996. Society of Petroleum Engineers
- 5.8.6 Naturally Fractured Reservoir, 4.3.4 Scale, 4.1.5 Processing Equipment, 5.5.8 History Matching, 1.8 Formation Damage, 5.2 Reservoir Fluid Dynamics, 4.1.2 Separation and Treating, 2.4.3 Sand/Solids Control, 1.6.6 Directional Drilling, 3.3.1 Production Logging, 5.5 Reservoir Simulation, 5.6.9 Production Forecasting, 5.6.3 Pressure Transient Testing, 1.11 Drilling Fluids and Materials, 5.5.2 Core Analysis, 1.6.9 Coring, Fishing, 4.6 Natural Gas, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 5.1.7 Seismic Processing and Interpretation, 1.6 Drilling Operations, 5.6.4 Drillstem/Well Testing
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This paper presents a discussion and interpretation of a variety of transient pressure responses observed in nine flow and build-up surveys performed in horizontal wells in the Sole Pit area fields Barque and Clipper.
The variation in pressure transient response from one well to another may be explained by facies variations in both a lateral and vertical orientation, and by the presence of natural fractures, sometimes located in dense conjugate clusters separated by matrix, and occasionally existing as discrete large sub-vertical fractures.
Horizontal well pressure transient flow regimes and signatures associated with heterogeneous reservoirs are observed in the survey log-log pressure derivatives. Rapidly declining transmissibilities in the vicinity of the wellbore are observed in two surveys, while other survey log-log derivative responses suggest a dual porosity characteristic followed by horizontal well intermediate time linear flow. Large individually discrete sub-vertical fractures are believed to provide a pressure response normally expected from hydraulically fractured wells with fracture wall skin.
Pressure transient testing contributes to an understanding of the reservoir behaviour by revealing essential characteristics of a flow model that can describe flow in the heterogeneous, fractured sandstone. Reservoir parameters defined from the test analyses were used in the construction of a full field
A number of papers have been published on horizontal well pressure transient analysis theory; and a few papers have dealt with test interpretation in oil wells. This paper, however, is unique in it's extensive discussion of the application of the theory in gas well testing in horizontal wells in heterogeneous reservoirs, based on a comparatively large data set.
Shell U.K. Exploration and Production is developing, on behalf of Shell and Esso the tight dry gas Rotliegend reservoirs of Barque and Clipper, located in the Sole Pit Basin of the U.K., Southern North Sea (figure 1). Well productivity is fundamentally dependent on the intersection of dune slipface sands and / or sparsely distributed open natural fractures. The initial development plans were based on conventional deviated wells, relying on massive hydraulic fracture stimulation, if required, to achieve economic production rates. The development strategy has progressively evolved towards the use of horizontal wells which increase the probability of intersecting the productive features in the reservoir. Some 16 horizontal wells had been drilled by end 1994, out of a total of 30 development wells.
The initial deliverability of the horizontal wells is significantly higher than that of deviated wells; productivity improvement factors of between 2 and 7 have been realised. The medium to long term well performance, however, depends on the well and reservoir boundary geometry, the reservoir quality, characteristics, variability, and connected gas in place. Pressure transient testing can contribute to an improved understanding of the reservoir production mechanisms and to the development of a reliable reservoir simulation model for accurate production forecasting and future infill well trajectory. Transient tests in horizontal wells provide near wellbore geometric average permeability and mechanical skin (Sm) for the productive length of the wellbore Lw.
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