High-Viscosity Crude Squeeze - An Effective Gas Shutoff Technique
Authors: McWilliams Jack B. 
Published: December 2007

The use of viscous crude oil is a less expensive means of controlling producing GOR's than most conventional methods. In addition, relative producing GOR's than most conventional methods. In addition, relative permeability to gas can be reduced without disturbing the relative permeability to gas can be reduced without disturbing the relative permeability to oil, and additional perforated intervals that previously permeability to oil, and additional perforated intervals that previously were isolated behind packoffs can remain open to production.

Introduction

Effective control of producing gas/oil ratios (GOR) is of primary concern in maintaining reservoir pressure in fields under secondary gas injection operations. Since the secondary operation depends on effective sweep, a very important variable is the fraction of the reservoir that has been flushed by the injected gas before gas breaks through at the producing wells. This "volumetric sweep factor" is a function of two conditions the position of the injection and production wells, and the permeability distribution in production wells, and the permeability distribution in the reservoir. The Embar-Tensleep reservoirs, discussed here, are under crestal inert gas injection and peripheral water injection. Through gravity drainage, the high relief of the reservoir also contributes to the recovery mechanism. The exploitation program practiced in the reservoir consists of injecting gas into the crest of the reservoir to maintain pressure and prevent solution gas from breaking through. This program minimizes dynamic pressure drops, which could change the characteristics of both the gas and the oil phases and thereby hamper the immiscibility of the fluids. In March 1972 there were six crestal gas injectors injecting 16 MMcf/D and 8 perhipheral water injectors injecting 7,500 BWPD. Presently, only five gas injectors remain in operation (Fig. 1). Gas/oil contacts are monitored effectively by periodic well testing. This contact observance is vital periodic well testing. This contact observance is vital to the prediction and improvement of sweep efficiencies. Reservoir pressure is also analyzed periodically since pressure sinks, when introduced into the system, tend pressure sinks, when introduced into the system, tend to influence gas movement and hamper ideal sweep conditions. As the gas/oil contact migrates downstructure, wells with production approaching established GOR limits must be dealt with. This may be handled with workovers or by simply shutting the wells in as high-GOR wells. GOR limitations are established in the Embar-Tensleep reservoir to maintain reservoir pressure. If the well influenced by the approaching gas/oil contact has not completely gone to gas, workovers are generally preferred because production, although often impeded, can continue. Many production, although often impeded, can continue. Many approaches have been attempted to deal with GOR control, each with varying degrees of success. A few of the conventional techniques practiced in Elk Basin to control gas producing zones include packer installations, scab liner installations, water injection, and cement squeezes. The most recent and most successful technique is the use of high-viscosity crude squeezes to reduce relative permeabilities to gas. High-viscosity crude squeezes possess many advantages over the conventional techniques mentioned above. Eight field cases are presented for discussion. Selection, application, presented for discussion. Selection, application, results, and economic considerations are presented for evaluating the method.

History

The Elk Basin field is situated approximately 20 miles north of Powell, Wyo., on the border between Wyoming (Park County) and Montana (Carbon County).

JPT

P. 551