Wireline formation testers are corrently widely used in open holes while through-casing formation testing is still in its early stage of application.
In this paper, a case history is presented where formation pressures are acquired through-casing in the Khuff deep gas formation. Considering the Khuff formation in Saudi Arabia and associated drilling difficulties, formation testing in open hole conditions can be quite challenging. In this field example, formation testing in an open hole was initially planned; however, drilling conditions did not permit open hole formation testing. Hence, a through-casing formation tester was utilized for the first time in Saudi Arabia to obtain important formation pressure measurements to assess pressure regimes in a reservoir with different layers. The through-casing formation tester anchors itself within casing, sets a packer element, drills a hole in the casing and through the cement and formation, performs pressure testing and or sampling, reseals the hole, pressure tests the mechanical plug and then frees itself from the casing to move to next testing interval. One of the challenges of through-casing formation testers is cement integrity behind the casing. Cement evaluation logs were run prior to the formation tester run. It was found that cement was patchy across the zone of interest. The through-casing formation tester was run over carefully selected intervals, and nine holes were drilled and plugged successfully in three wireline runs. After the jobs, leak tests of 4000 psi differential were carried out and confirmed the casing integrity.
Results showed interesting pressure differences among different layers with similar pressure trends observed in near by wells. The operational challenges, observations and recommendations for future applications are discussed in this paper.
It is known that formation pressures can provide extremely useful information about reservoir drainage and communication among different reservoir layers and this information can significantly impact reservoir development. Formation testing in open holes has been used regularly to obtain formation pressure identify/characterize mobile fluids and to collect representative fluid samples. This evaluation may not be possible when open hole conditions do not permit logging. Advances in formation tester technology and development a novel electro-mechanical drilling technique have provided the oil industry with a new modular through-casing formation tester.