Pressure- and rate- transient analysis of the simulated single and multi-fractured horizontal wells drilled in shale gas reservoirs

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2013
Jafarlı, Tural
Nowadays, the bigger portion of produced oil and gas come from conventional resources all over the globe and these resources are being depleted in a severe manner. Over the past decade, the combination of horizontal drilling and hydraulic fracturing has allowed access to large volumes of shale gas that were previously uneconomical to produce. In recent years, they are seriously considered as supplementary to the conventional resources although these reservoirs cannot be produced at an economic rate or cannot produce economic volumes of oil and gas without assistance from massive stimulation treatments, special recovery processes or advanced technologies. The vast increase in demand for petroleum and gas has encouraged the new technological development and implementation. With the directional drilling technology, it is possible to make use of highly deviated wellbores, extended reach drilling, horizontal wells, multilateral wells etc. Along with the technology itself simulation, reservoir characterization and the ability of future production prediction makes the development of unconventional resources a lot easier. In this study, pressure and rate transient analysis techniques developed for hydraulically fractured reservoirs were applied for shale gas reservoirs to understand the applicability of those methods on unconventional systems. Pressure transient analysis is based on the analysis of the pressure which changes over time with variation of the fluid flow rate. For the particular analysis, fluid allowed to flow for a limited time, then well is closed and the pressure behavior is monitored and recorded in order to analyze the data. Rate transient analysis refers to production data analysis which utilizes similar concept to pressure transient analyses. It is similar to drawdown test where this drawdown period is equal to producing life of a particular field, where the flow periods are interrupted by shut-in periods, with less frequent data acquisition which is why the data quality for the analysis is not as good as for pressure transient analysis. Schlumberger Eclipse 300 simulation model was used to model the shale gas reservoir. Two commercial software tools – Saphire (Kappa) and F.A.S.T. (Fekete) that are used in petroleum engineering were applied to analyze the data. Advanced analytical models (F.A.S.T.) developed for horizontal multi-fractured reservoirs showed some good results; however it still doesn’t clear what are the actual flow regime conditions under different fracture stage and flowing conditions. In general those tools analyze the data to match either linear, bilinear or boundary dominated flow conditions. For that reason, in order to clearly understand flow regimes, rate normalized pressure derivative function was adopted along with the corrected pseudo-time function. As a result of this straight line analysis - flow regimes, fracture and reservoir permeabilities, fracture half length, fracture conductivity parameters were found under different fracture stage and flowing conditions. Under constant rate producing conditions, for single fracture case we obtained – fracture linear, elliptical, radial and late time effects, however for multi-fracture example, elliptical flow regime was masked due to close fracture spacing and additionally compound linear flow parallel to hydraulic fractures were exhibited. Under constant bottom-hole pressure producing conditions, for single fracture case we obtained pseudo-steady state flow showing pressure depletion in the stimulated reservoir region, radial flow, boundary dominated flow conditions, while for multi-fracture case we additionally observed compound linear flow regime.

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Citation Formats
T. Jafarlı, “Pressure- and rate- transient analysis of the simulated single and multi-fractured horizontal wells drilled in shale gas reservoirs,” M.S. - Master of Science, Middle East Technical University, 2013.