Well-Test Logging Allows Low-Cost Dynamic Characterization, Value Optimization

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 206177, “Piloting the First Well-Test Logging in the Middle East, Paving the Way to Low-Cost Dynamic Reservoir Characterization and Well-Value Optimization,” by Raymond Nguyen, SPE, ADNOC, and Antoine Jacques and Vincent Jaffrezic, SPE, TotalEnergies, et al. The paper has not been peer reviewed. The development of carbonate reservoirs in a giant field offshore Abu Dhabi requires long horizontal wells but carries the risk of unwanted gas and water channeling through its inherent heterogeneities. Success depends heavily on the quality of the formation knowledge before completion. Well-testing logging (WTL) offers the advantage of recording a log of mobility at the end of the process of drilling the openhole, enabling favorable timing to influence adapted completion and stimulation design. Field and Geological Background The studied field is northwest of Abu Dhabi. It has a gently dipping domal asymmetric anticline structure. Two reservoirs of interest are discussed in the complete paper, the first characterized as Early Cretaceous and the second as Upper Jurassic. The first of these, Formation K, is separated into two thick segments, Upper K and Lower K, divided by a laterally continuous stylolitic boundary, representing one-third and two-thirds of total K thickness, respectively. Upper K has a depositional setting of foreshoal to shoal, whereas Lower K has a depositional setting of a middle ramp environment with moderate water depth, mainly consisting of argillaceous material. Within the Upper Jurassic group, the formation of study was deposited in a multiple regressive cycle and can be divided into four major stratigraphic layers, the shallowest being A_1 and the deepest being A_4. Each of these layers has its own unique petrophysical properties; however, the complete paper focuses on a sublayer within A_1. Because of the cyclic pattern of sea-level fluctuations at shallow depths, the main depositional lithologies were limestone, dolomite, and anhydrite, with limestone and dolomite being the reservoir and anhydrite acting as the seal. The average thickness represents approximately a tenth of the formation’s thickness. The development scheme of the tighter reservoirs, K and A_1, in the coming years is based on patterns of parallel horizontal oil producers and water injectors to bring closer pressure support. Pattern development is directly affected by heterogeneity that could cause premature water breakthrough. Enhanced conformance with customized completion design and selective stimulation can mitigate these phenomena. These developments have been piloted recently with the drilling of long horizontal producers, Well_1 in K and Well_2 in A_1. The WTL technology was piloted for the first time in the Middle East in these wells.