Deep-Conformance Control Improves Sweep Efficiency in Mature Waterfloods of the San Jorge Basin
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 129732, ’Deep-Conformance Control by a Novel Thermally Activated Particle System To Improve Sweep Efficiency in Mature Waterfloods of the San Jorge Basin,’ by J.L. Mustoni, SPE, Pan-American Energy; C.A. Norman, SPE, Tiorco; and P. Denyer, BP plc, prepared for the 2010 SPE Improved Oil Recovery Symposium, Tulsa, 24-28 April. The paper has not been peer reviewed.

Six pilot applications of a thermally-activated-particle (TAP) system were applied in mature waterfloods in the San Jorge basin (SJB), Argentina. Injected water preferentially flows along the center of the channel, which becomes a “thief zone,” and breaks through to the producers prematurely, leaving much of the oil unswept. Particle technology has blocked thief zones deep in the reservoir. This blocking creates a new pressure gradient in the reservoir that promotes diversion of injected water toward zones with higher oil saturation.  

Introduction

SJB waterfloods are characterized by low recovery efficiency because of an adverse mobility ratio and the reservoir-rock spatial anisotropy. This heterogeneity is typical of fluvial systems with high contrasts of rock properties inside the same channel body. A permeability contrast of 5:1 between the center and the edge of the channel is typical. The three operating contracts are in southern Argentina and cover approximately 3500 km2 and include 3,800 active oil and gas wells producing from an average depth of 2200 m.

As of June 2009, production totaled 17 800 m3/d of oil and almost 9×106 m3/d of gas. Approximately one-half of the oil production is attributable to a massive secondary-recovery (waterflooding) operation that injects 27 000 m3/d of water through 620 water-injection wells. Reservoir heterogeneities and the adverse mobility ratio typically increase the water/oil ratio (WOR) to greater than 10 within a few years of startup. Substantial oil is bypassed by injection water and is the target for a new technology to improve sweep efficiency.

Complexity of SJB Reservoirs

Sand bodies are separate hydraulic units with distinct reservoir pressures and fluid and rock properties. Depending on well location, the total column thickness varies from 400 to 3500 m and can include up to 30 separate reservoirs that are segregated vertically by water-saturated sandstone layers or impermeable shales. Each hydrocarbon trap is relatively small volumetrically, and most channels are 200 to 700 m wide and 3 to 10 m thick. Because areal continuity is limited, adjacent wells are likely to contact different reservoirs or the same reservoir with different petrophysical characteristics. Therefore, pattern configuration is irregular in an attempt to follow the geometry of the productive reservoirs. The injector/producer flow model is unique for each pattern, depending on reservoir heterogeneities, rock/fluid properties, location of the wellbore within the contacted reservoirs, and the number of productive reservoirs present in the injector and associated producers.