Formation Evaluation and Reservoir Development Optimization by Multi-well Deconvolution Driven Multiwell Retrospective Testing (MRT)

Abstract

An off-shore field in SE-Asia has high reservoir heterogeneity and consists of several highly permeable layers. The current field development challenges are to evaluate the potential for additional drilling and reveal the potential of production increase by injection optimization. Good Understanding of cross-well reservoir connectivity at the area, the shape and size of existing wells drainage area, reservoir properties distribution and cross-well pressure impacts are the key points for additional drilling projects and production enhancement.

A1 reservoir in this field was at the focus of the study. This reservoir produces light oil and with the decrease in formation pressure, gas production has increased. A Multi-well Retrospective Testing (MRT) service was applied based on historical well pressure and production data to evaluate the reservoir compartmentalization, quantify well interference and drainage area. Historical data over 12 years (2007 to 2019), from an area consisting of 4 producers and 1 injector was analyzed using MRT. MRT extends the technique of single-well deconvolution to the analysis of pressure and production data to a group of wells. MRT was used to evaluate reservoir transmissibility between wells, cross-well interference, formation pressure history, productivity index dynamics and well drainage area. The deconvolved single unit-rate pressure drawdown transient recovered by multiwell deconvolution was interpreted to calculate formation properties around the pressure-tested well (self-transient response) and cross-well properties between offset wells (interference test response). This self-transient response is free of interference from dynamic boundaries of surrounding wells. Its interpretation by pressure transient analysis provided well drainage area, shape and aquifer/gas cap support for the well. Cross-well pressure transient responses revealed reservoir transmissibility between wells. MRT analysis found that all the offset wells were connected to the focus well. the reservoir transmissibility of the connected part of the formation between the wells was lower than expectations from open hole logs.

MRT revealed weak pressure support from the aquifer and gas cap, that was insufficient to compensate field pressure for current throughputs. A formation pressure depletion trend was calculated resulting in gas liberation. However, the well drainage area was found to be extensive than expected. This could indicate a possible reservoir extension perhaps in the north-east direction. Further Geological and geophysical studies are required to address the uncertainties in the area.

The results of the MRT study were used as inputs for numerical cross-well pressure modeling and then translated to conventional reservoir modeling language, to try to obtain a better understanding of MRT measured reservoir properties. he information from MRT study as used to optimize upcoming infill locations and other opportunities for production enhancement: well stimulation and injection increase.