Retrospective Study and Multidisciplinary Optimization Workflow to Address Production Challenges in Ultralow Permeability, Tectonically Active, HPHT Dolomite Formation in Northern Kuwait

Abstract

The deep high pressure/high temperature (HPHT) dolomite formation in Northern Kuwait has been a challenge with varied production, attributable to reservoir heterogeneity. Due to the tight nature of these rocks, matrix acidizing may not produce desired effects, thus requiring hydraulic fracturing to produce at economic rates. However, the tectonic setting in high stress environment has resulted in subpar success and inconsistent results from stimulation treatments in matrix and hydraulic fracturing applications. This paper presents a multidisciplinary approach to address the limited success in the Northern Kuwait Dolomites. An integrated petrophysical evaluation of the current wells will be followed with multi-well Heterogeneous Rock Analysis (HRA), to evaluate the reservoir heterogeneity across the field and identify the ‘sweet spots’ for future drilling locations. Evaluation and lessons learnt from the past stimulation treatments, will be used to understand geo-mechanical challenges and to help calibrate the Mechanical Earth Model (MEM) for implementation in the future wells. Finally, using a reservoir-centric stimulation design tool, stimulation type (acid fracturing vs proppant fracturing) and stimulation design optimization for future wells will be developed. A reservoir-level petrophysical evaluation of the existing wells was performed and compared to understand the reservoir heterogeneity vis. a vis. production potential. Multiple rock classes were identified within the tight dolomite interval, with a gross thickness of ~250 ft. Starting with log based MEM, results from the image log interpretation and the field observations/measurements from fracture diagnostic tests (Decline analysis, Calibration injection) were used in calibrating the MEM and mapping the Completion Quality (CQ) heterogeneity across the field. This has led to a reservoir-level understanding, which can enable planning optimal well locations, target interval and subsequent well placement/completions methodology. Finally, using the reservoir-centric design tool, an optimum design to effectively stimulate the ultralow-permeability dolomites was determined. The optimization workflow did not only include a single-faceted approach of fracture modeling, but also encompassed a production forecast using the integrated numerical reservoir simulator. Lessons learnt from the optimization workflow were further extended to designing horizontal wells (landing point, trajectory for optimal stimulation geometry), and hence to aid in field development strategy. Using the multidisciplinary unconventional workflow, the heterogeneity in reservoir quality and completion quality was evaluated, both along the wellbore and spatially. In essence, we found that natural fractures along with high Critical Net Pay (CNP) allows you to vertically connect with good RQ and thus, is required for success in these tight reservoirs. Following which, reservoir-centric stimulation design tool enabled optimization of completion and stimulation design in a holistic approach, to maximize appraisal and production opportunities.