Well testing is very challenging especially in northern parts of Pakistan, as there are complex lithologies and multiple formations encountered in a single well. These formations include both fractured carbonates and sandstones. In addition, lower matrix porosities make it more difficult and time consuming as it can take several weeks to months to test multiple formations individually using a casedhole drillstem test (DST). These tests impact the overall well cost due to the extended rig time required and production loss. Extended buildups are a huge concern that must be kept in consideration due to the high rig-time requirement. This paper describes the application of a wireline formation tester (WFT) for interval pressure transient testing (IPTT), which is also referred to as a mini-DST, to estimate flow regimes and reservoir properties along with vertical pressure profiling, fluid identification, and sampling. This technique was applied at two of the exploratory wells in TAL block. There, WFT was deployed with a single probe and straddle packers to achieve the desired results across four potential reservoirs. Vertical pressure profiles across the prospective formations were acquired using the single probe; this was followed by a mini-DST using straddle packers to test zone by zone for fluid type, collect samples, and record pressure buildups. Real-time pressure derivatives were monitored to optimize the buildup time at each station depth. This integrated IPTT gave necessary reservoir information in a very short span of time. It saved significant amount of time and costs, especially rig costs and entire well testing cost giving valuable information for completion strategy.
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.
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