Field Application of a New In-Depth Waterflood Conformance Improvement Tool

Abstract

Abstract An Industry Consortium (BP, ChevronTexaco and Ondeo Nalco Energy Services) conducted a multi-company research project known as Bright Water. The goal of this project was to develop a time-delayed, highly expandable material that would improve the sweep efficiency of a water flood. In November 2001, the first of these water flood profile modification treatments was pumped in the Minas field. The Minas Field, located on the island of Sumatra in Indonesia, has an OOIP of 8.7 billion barrels, is at nearly 50% recovery, and has water-cuts greater than 97%. Reservoir thief zones have been identified throughout the main reservoir layers. The main objective for pumping a profile modification material is usually to divert injected water out of thief zones and into zones with higher oil saturation, though areal sweep improvement can also be expected. The profile modification treatment of 42,000 barrels water containing 4500 ppm of active material was pumped into Minas injector 7E-12 ("A1" sand). The objective of the field trial was to verify that significant volumes of this low cost material could be pumped deep into the reservoir at low viscosity, and then expand after a pre-designed time interval. Injection tracer studies were conducted pre- and post-treatment to aid in determining changes to the injection sweep efficiency. A bottom hole pressure fall off test was also used to measure post - job permeability. The trial demonstrated that large volumes of the material can be pumped into the formation without raising the injection pressure or blocking the injection well bore, can propagate in the rock pore system, and then will expand at a pre-designed time. Changes in oil production after the trial will be discussed along with the field data acquired during and after the trial. As part of the continued development of this material, a second trial commenced in late November 2002 on a North Sea (UK) production platform. The treatment was successfully placed in mid December, 2002. Introduction This paper presents a case history in which a novel profile modification treatment was pumped in the Minas waterflood. Of all the problems that can beset oil wells, unwanted water production is one of the most troublesome, yet water flooding to improve the recovery of oil is the most common secondary recovery process used in the modern oil industry. Water production causes many problems such as corrosion, scaling, cost of oil water treatment and cost of disposal. In water injection projects excess water production is often linked to poor sweep efficiency, which renders significant amounts of oil irrecoverable during the economic life of a field. Poor sweep efficiency can be the result of zones with unfavorable permeability in heterogeneous reservoirs or unfavorable mobility ratio within homogeneous rock. Specifically water can break through from the water injection to the oil production wells in the most permeable zones while significant oil is left in the reservoir (Fig. 1) or it can pass through low mobility oil by a process of viscous fingering.1 The problem can be even more severe when bottom water zones with high water saturation and therefore variations in relative permeability exist. 2,3