ABSTRACT
Shale gas is a new horizon in Pakistan to meet growing energy demands. Comprehensive data gathering is mandatory for proper evaluation of a shale gas play and to determine feasibility of a prospect. Shale reservoirs require hydraulic fracturing to produce commercially. In Pakistan, stresses are normally high due to plate tectonics. In some cases, the lack of sufficient understanding of stress conditions has led to failures of full hydraulic fracturing operations.
Stress testing is a technique used to evaluate formation breakdown pressures and minimum in-situ stresses. Stress profiles can be estimated using openhole log data, however direct in-situ measurement is needed for calibration. Wireline formation testers have been used in the field to measure formation pressures, estimate mobility and obtain good quality downhole samples. One of the advanced applications of the wireline formation testers is to measure insitu stresses in a wellbore to calibrate the mechanical earth model (MEM) and to design a feasible hydraulic fracturing job.
Traditional wireline insitu-stress technique has been around for some time now, however the technique suffered from a limited pressure ratings, which was not enough to breakdown the formation. An advanced wireline formation tester module capable of achieving a break down through sleeve fracturing at a very high pressure was used for stress measurement for first time not only in Pakistan but worldwide. The technique involves setting a single packer module across the target shale zone and inflating the packer until the formation breaks down. Once formation break down is achieved, either a straddle packer is set across the target formation and injection is performed for fracture reopening, or another cycle is done with the single packer element to record sleeve reopening pressure.
Detailed planning was done by the reservoir and geology departments. Four tests at four different locations were done in the target well where formation break down pressure, closure and fracture re opening pressures were estimated. This information is used for updating a 1D geomechanical earth model for the further use in planning full scale hydraulic fracturing treatment.
