Stimulation Feasibility Study Based on 3D Geomechanical Modelling on Thin and Tight Reservoir with Thin Cap Rock

Abstract

The field is located near the UAE capital, Abu Dhabi, with a tight oil and gas bearing carbonate formation. Rapid pressure drop observed, indicates slow charging from reservoir. Typically a tight reservoir like this is developed by hydraulic fracturing. However there is concern of fracture containment and placement. This study was conducted to construct a 3D reservoir geomechanical base model to optimize the completion strategy and production performances for the tight reservoir.176 laboratory tests/measurements on cores were performed to determine the mechanical properties and petro-physical properties at different intervals in 5 wells over the field. Eight 1D mechanical earth models (MEMs) were constructed to characterize the mechanical properties and stresses along the well trajectories, and the laboratory test results were used to calibrate the mechanical property profiles of the 1D MEMs. A 3D geomechanical model was constructed using seismically-interpreted horizons and faults; mechanical property population and boundary stresses were based on the 1D MEMs. Present-day stresses within the formation and surrounding formations were simulated, and stress evolution from 2011 to 2095 was predicted. Preliminary fracture modelling was performed at two wells to understand feasibility. The major concern is to control fracture containment within the reservoir section, particularly avoiding downward growth. The results indicate that there is tendency of fracture growth downward at one well. However, the downward fracture growth at the other well is not expected. The average upward stress barrier is around 400 psi over the field and the average downward stress barrier is around 800 psi. However, the magnitude varies from location to location. Five completion methods were compared in terms of geomechanics. Acid tunnel and fishbone completion have a very low risk in horizontal well stability. Multilaterals completion has a low risk in horizontal well stability and junction integrity. Acid fracturing and proppant has a relative high risk in fracture placement and containment. It is recommended to perform further completions feasibility study to review the feasible well location, productivity enhancement, economical aspect and operational constraints.This study reveals that the heterogeneity in the carbonate reservoir has a significant impact on the selection of completion methods. There is a high uncertainty to decide an optimal completion strategy based on 1D geomechanical study results because the large variations in the in-situ stress and mechanical properties. Therefore, a 3D geomecanical study is necessary for the completion selection for heterogeneous carbonate reservoirs, particularly for tight thin plays.