Multilateral Wells to Control Water Inflow in Reservoir Connected to Active Underlying Aquifers: A Technical and Economic Analysis

Abstract

Abstract In formations with good storage and flow capacity connected to underlying aquifers with strong water intrusion due to the absence of geological seals, conventional primary or enhanced production techniques do not seem to solve the aquifer's water encroachment problem. This work presents the technical and economic analysis of the use of wells with multilateral architectures as an alternative to overcome the uncontrolled water inflow from active aquifers and its consequences on oil productivity. To analyze the production options of an area with strong water influx in a Colombian field, different configurations of multilateral wells were studied considering the governing flow mechanisms in the reservoir. To do so, a numerical simulation workflow was proposed, using local grid refinement analysis to guarantee the representativeness of the active aquifer inflow phenomenon and the operating parameters that maximize the performance of these wells were determined through sensitivity analysis. The results of this study demonstrate the potential of the technology to increase oil production and ultimate oil recovery by adequately managing the drained water from the aquifer in a cost-effective manner. A well drilled in an unsealed area with strong aquifer inflow quickly exceeds the 99% water cut and must be shut after a cumulative production of only 40000 BBL of oil. This is the case of more than 5000 Mbbl of oil stored in Colombian fields, connected to very active aquifers that currently cannot be produced economically. Bilateral or multilateral well configurations allow, simultaneously, oil production in the interest area and the creation of a water drainage area below the oil-water contact. In this way, it is possible to mechanically control the water inflow to the oil-producing segment, keeping the water cut below the economic limit (99.5%), increasing the cumulative oil production, and extending its productive life. As for the drained water, there are several management options, either producing it to the surface or reinjecting it into a nearby (upper or lower) formation. The results of the numerical analysis show that the oil production of a well located in an unsealed zone with strong water encroachment, can increase more than 7 times if the proposed drainage segment support is used in the multilateral configuration. It is possible to keep the water cut below the economic limit and increase the well productive life.