Use of Multi Detector Pulsed Neutron Technologies to Address the Challenges with Saturation Surveillance in Rumaila, Iraq

摘要

Rumaila, Iraq, is one of the biggest oil fields in the world, producing through multiple stacked clastic and carbonate reservoirs and relying on several recovery mechanisms such as natural aquifer drive and water flooding which have changed the initial fluid distribution. To evaluate the change of fluids distribution, multi-detector pulsed neutron (MDPN) instruments are run within the field. MDPN measurements require careful interpretation accounting for logging conditions and formation environments to provide an accurate result of multicomponent fluid saturations so well work activity can be optimised, and production and recovery can be maximized. Compatibility with legacy data is also critical for use in time lapse evaluations. Recently, the MDPN technology diversified with more instruments being developed. Field trials are required to understand backwards compatibility for some of the common nuclear attributes as well as benchmarking and calibrating the nuclear models with the in-situ measurements. While all share the same physics principle, the responses can vary owing to instrumentation design, characterization and nuclear attributes extraction in the field. We will present the data integration approach taken by the production team using historical and latest generation MDPN data, some acquired for the first time in the clastic and carbonate formations of Rumaila field. The paper will describe BP's in-house workflow customised for MDPN derived saturation in Rumaila. This will address the nuclear attribute screening and selection process for the two types of reservoirs (clastic and carbonate) and the associated displacement mechanisms. Data from multiple MDPN instruments are used to illustrate the robustness of our workflow that accounts for borehole configuration, formation properties, reservoir fluids properties and detailed nuclear models for each tool. The nuclear model driven interpretation showed that logging conditions and reservoir properties can significantly impact the accuracy of fluid saturation. The uncertainty in MDPN derived saturation can be reduced if the deviations from notional values are known. Because of similar sand-clay properties, the carbon oxygen response in the clastic reservoir showed a unique pattern challenging the conventional understanding of such data. Additional to reservoir complexity, new challenges will be faced in relation to wellbore access because more wells are completed with electric submersible pumps (ESP). In ESP completed wells, the access to reservoir section will be thru Y-tools using slim MDPN instrumentation. Our study identified the optimal procedures and best nuclear attributes that can be logged in these conditions without increasing the saturation uncertainty.