Formation Pressure Evaluation for Producing Wells Without Shutting Down the Well, Using Multi Rate High Precision Temperature and Spectral Noise Logging (HPT-SNL)

Abstract

Majority of the oil and gas fields in the UAE are mature multi-layered carbonates reservoirs, which determines complex vertical heterogeneity and challenging development of those reservoirs. Conventional methodology to measure sublayer pressure is to utilizing different wireline formation testers for any new well or worked over well before commissioning for production. Once well is completed and put on production; usually the average reservoir pressure is measured at the depth of perforation using conventional pressure build up (PBU) or bottomhole closed-in pressure (BHCIP) methods. Using conventional approach it is always difficult to understand which layers are more depleted than others, as only average reservoir pressure is recorded in the wellbore. In case of the heterogeneous multi-layer reservoirs, pressure measured conventionally in the wellbore will be at most of the times, inadequate for sublayer pressure estimation. This paper will describe new methodology of formation pressure evaluation, as well as real case study done in one of the developed offshore carbonate field in the UAE. This method allows measuring each sublayer pressure for producing wells without interruption of the production and properly defining any differential pressure between sublayers. This will help when applying any gas shut-off or water shut-off techniques and prolong the life of producing wells, as well as to help future development of the field. The determined reservoir pressure for each layer has been compared with recent formation pressure tester measurements obtained for this well. The pressure measurement is in the range of 20 psi tolerance. Identification of sublayer reservoir pressure for each producing interval is vital for highly heterogeneous multi-layered reservoirs. This technique is important for gas and water production management when one or several sublayers become depleted. Appropriate action for gas/water shut-off technique can be applied in the right time which will help to manage reservoir efficiently, as well as reducing the cost for conventional pressure measurements and eliminating the loss of production due to shut in time for pressure stabilization during conventional BHCIP or PBU.