Flexible Multi-Well Interference Test Design for a Deep-Water Field

Abstract

Interference testing is a common tool for addressing reservoir connectivity and compartmentalization risks. Due to the high costs of deep-water and ultra-deep-water extended well testing, this type of test is rarely performed during the appraisal phase and is usually postponed until the start of the field development. With the infrastructure in place, testing can be carried out with minimum planning and at a minimum cost. This is generally acceptable for fields with a lower subsurface complexity. However, for complex turbidite fields, this information becomes critical at the appraisal and early development planning stages to reduce the risks in depletion optimization and production infrastructure planning. To make testing practical, it has to be performed in a way that minimizes rig time and de-risks collection of required data. To optimize the interference test design for the West Africa deep-water field appraisal phase, a simulation study was carried out to assess the impact of major uncertainties. A fine-scale 3D simulation model was used due to high heterogeneity and complex connectivity between individual channels and channel complexes. Impact of the drawdown rate, flow duration, tidal effect amplitude, OWC, faults transmissibility, absolute permeability, reservoir pore volume, and zones connectivity on interference time for different selections of test and observation wells were assessed through the sensitivity runs. Results were analyzed to get a better understanding of reservoir dynamic response such as pressure travel time and potential interference between zones. Based on this study a flexible interference test plan was defined that ensures optimal rig use and minimal risk of sub-optimal dataset collection. This plan embeds both pre-test decisions and real-time decisions that depend on early time observations. An optimal test and observation wells setup that provides a balance between the rig time and value of information will depend on the planned appraisal well results and is one of the decisions to be finalized before the test. However, decisions on flow duration adjustment and consequent data monitoring in the observation wells will be made based on a set of early time events identified from the sensitivity of pressure interference response between different zones and wells. The proposed uncertainty driven approach provides an obvious advantage over the common test design based on the "best technical estimate" model. It also provides a better basis for test feasibility decision and cost-effective implementation.