Abstract
Advances in formation tester technology and a novel electro-mechanical drilling technique have provided the oil industry with a new modular through-casing formation tester. The wireline-conveyed tester, which determines formation pressure and fluid content behind casing, has been developed in a joint project conducted by the Gas Research Institute and Schlumberger. More than 200 Tcf in gas resources are estimated to exist behind casing in the United States alone. To facilitate evaluation of these potential reserves, the tool was designed to make a hole through the casing, measure formation pressure, take fluid samples and then reseal the hole. This paper describes the tool features, applications and field test results.
Primary applications include detection of bypassed hydrocarbons, evaluation of potential pay prior to well abandonment, and formation testing under conditions where openhole testing and sampling are not feasible. Reservoir management applications include production monitoring, especially waterfloods and CO2 floods, and economic evaluation for selling and booking reserves. Secondary applications include detecting gas-collector zones in gas storage wells, and injecting or producing through a few small drilled holes (i.e., limited-entry steam injection).
The tool uses a flexible drill shaft to drill holes several inches deep through casing, cement and formation. Pretests, involving pressure drawdown and buildup flow periods, are performed as pressure is measured with both a crystal quartz gauge and a strain gauge. If desired, a formation fluid sample can also be taken at this time. A reliable mechanical plug seals the drilled hole in the casing, creating an effective seal to at least 10,000 psi of differential pressure (either direction). This service was introduced in October 2000 and is now completing field trials. This novel technique for measuring pressure and taking samples through casing provides the ability to assess pay without perforating the well and facing costly and often problematic cement squeeze jobs.
