An Integrated Workflow to Close Out the Uncertainties in a Geomechanical Model in a Giant Onshore Carbonate Gas Field in Abu Dhabi, UAE

Abstract

Abstract A giant lean gas reservoir overlying a large oil rim is producing for more than 27 years became under depletion mode without any pressure maintenance. Formation collapse in reservoirs under depletion can cause permeability reduction, completion damage and well failure, reducing or even interrupting production and affecting the ultimate recovery from the reservoir. It is therefore critical to predict any risk in formation collapse. If such risks exist, recommendations are required to optimize reservoir management. Stress measurements were acquired and core analysis were performed in intact rocks area and used for 1D MEM (Mechanical Earth Model) and 3D MEM. 1D MEMs for 10 wells were constructed. Rock mechanical tests were conducted on core samples. 3D MEM was created with 13 interpreted seismic overburden horizons and 105 seismic faults. Four scenarios were performed to identify formation failure during the scheduled production. The worst-case scenario will happen of reservoir depletion, in case of weak formation and reactivated faults. Intensive logging, fracture modelling, coring program across the main fault corridor and RMT (Rock Mechanics Tests) were performed in vertical and horizontal holes across the fault corridor area to fulfil gaps of rock mechanical properties (elastic properties and rock strength) and field stresses. The acquired data were seeds for Lab testing, fracture network analysis and fault characterization which used to update the 3D MEM. Additional Lab tests to fill gaps in rock samples with high porosity (> 30%) were carried out and 1D MEM of 5 more wells were constructed, and the 3D MEM were updated. The 2017 updated 3D MEM eliminates three of the 2013 four scenarios and ended up with one robust scenario that shows better reservoir integrity and very small localized areas of pore collapse in high porosity regions only (> 30%) compare to the previous model. The reservoir can produce under depletion mode with production optimization in areas of expected compaction. Well integrity study and compaction monitoring are also considered to be commentary studies.