Learnings From High Rate Water Injection in Deep-Water Slope Channel Complex and Frontal Splay Turbidite Reservoirs Offshore Ghana

Abstract

Water injector wells are usually operated under fracturing conditions in deep-water turbidite reservoirs. Fractured injection is important to ensure high rates are delivered to sustain prolific oil producer wells. However, well rate is limited by the shale fracture pressure to avoid containment or reservoir management issues. Geology plays an important role in how these wells perform and behave. This paper highlights the differences when injecting under fractured conditions in deep-water turbidite reservoirs offshore Ghana, West Africa. Injectivity decline was observed in one field, and work was carried out to determine the root cause. Ultimately different injection strategies and well designs are required to sustain field performance, depending on the depositional setting and reservoir body geometry and fabric. This paper will present field data on injection performance and behavior, differentiating injection in frontal splay (lobe) - dominated and multi-stacked slope channel complex-type deep-water turbidite settings. Information includes: Conceptual geological framework to delineate reservoir body boundaries and their vertical and lateral heterogeneities that impact on fracture propagation; Pressure Transient Analysis; Fractured Modelling and History Matching to demonstrate impact of channel boundary effects; Geo-mechanical Model; Investigation into cause of injectivity decline and proposed solutions; Field trial results demonstrating impact of continuous high rate injection on inter-shale layers in multi staked reservoirs. Learnings from show that injectivity decline was not caused by impairment but should be expected when injecting at high rates into a ‘narrow’ reservoir, with multiple reservoir elements, laterally bounding shale intervals, and a thick, but internally rheologically variable cap rock. Hence, different injection strategies were employed, and a new ell design depolyed, depending on the geology, to sustain huigh rates. This paper investigates water injection under fractured conditions in different deep-water turbidite reservoirs. We outline the key steps taken to develop a sustainable injection strategy. As a series of case studies from different styles of turbidite reservoir body geometry, with variable quality and connectivity, it allows development geologists working on slope channel and frontal splay pools to gain insight into developing strategies that maximize recovery and manage heterogeneity impact on injection design,

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018