Cased Hole Production Testing with Extended Spacing Wireline Formation Testers

Abstract Wireline formation testing in open hole can yield robust and reliable information about reservoir fluid type and productivity. However, operational or logistical concerns can sometimes preclude gathering a full open hole formation tester data set. In this case the operator is left to either forgo the information or acquire the data in cased hole. Perforating and production testing in cased hole can be time consuming and expensive especially when there are multiple layers to be tested. This can be mitigated by using wireline formation testers (WFT) in cased hole to test individual layers, but these testers have traditionally been limited in their possible interval length. In this paper we discuss cased hole wireline formation testing with a unique configuration of the WFT that allows testing intervals much greater than previously possible. Wireline formation tester tools with straddle packers are typically limited to about 1-m spacing between the packers. With special adaptors spacings up to 3 m have been accomplished. However, when perforated intervals are longer than this the straddle packer is not an option: it is usually inadvisable to set the elements across perforated casing and cracks in the perforated cement can make the fluid typing ambiguous. This paper discusses a method whereby two separate straddle packer tools are combined and allow a significantly longer interval to be tested. We present a case study where the extended interval was tested and flowed for several days with the formation tester and a confident determination of fluid type performed. Additionally, a long build-up time enabled us to derive a robust estimation of permeability. The operation was concluded in three days versus the ten days of rig time that would have been expected for a cased hole production test. We also show how this method can be extended to longer intervals in both open and cased hole. We conclude that this method is should be considered for zones that could not be tested in open hole but are not worthy of a full production test in cased hole. Although cased whole WFT operations with straddle packers have been reported in the literature this is the first instance of a double WFT tool arrangement that allows testing layers of significant perforated length. Operational guidelines and environmental limitations are also discussed.