Resistivity Anisotropy and its impact on reserves estimates and technology applications in North Kuwait Reservoirs

Abstract

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractLaminated shaly sand sequences are often overlooked when determining pay intervals in clastic reservoirs. This is because traditional methods of calculating hydrocarbon saturations in these formations use resistivity measurements and one of the numerous shaly-sand saturation equations. These techniques generally understimate the hydrocarbon content because conventional resistivity measurements are dominated by the conductive component of the formation, in this case shale. Even when the excess conductivity due to the shale is accurately accounted for in the calculation, there is still a high degree of uncertainty in the results.Laminated sequences such as these are commonly found in the Burgan Formation in the Raudhatain and Sabiriyah Fields in North Kuwait. They have traditionally been considered as non-pay and the hydrocarbon content of marginally shaly formations has generally been underestimated.Recent work re-evaluating wireline log measurements in these fields, taking the shaly formations into account, has significantly increased the volume of hydrocarbons in place. However, there remained a high degree of uncertainty in the results. These new estimates can now be confirmed, and the uncertainty removed, by the combined use of vertical and horizontal resistivity measurements. The measurements, made using a multi-component induction logging tool, measure the electrical anisotropy of the formation, and as such can give a greatly improved measure of the conductivity of the thin sand layers within the laminated sequences. Additionally, these measurements can be used to determine whether the shaly sand is a laterally extensive laminated formation or a disturbed non-reservoir quality rock. This paper will review the technology used to acquire the measurements, show examples from the wells logged in North Kuwait, and describe the impact on reserves estimates. The paper also highlights a successful case of active interaction between KOC Field Development and Research & Technology Groups and Baker Atlas as a service company.