Warm Air Coking Sand Consolidation Field Results In Viscous Oil Sands
Authors: Fitzgerald Ben M. , Stephens Glynn , Terwilliger P.L. 
Published: December 2007

Warm air coking is a completion technique that has been used to prevent the production of sand into wells producing from unconsolidated sand formations. It is accomplished by injection of heated air into the formation around a producing wellbore until the crude oil becomes oxidized into an insoluble coke or resin which binds the sand grains together. In addition to stabilizing the loose sand, the heated air stimulates oil production. Results of several field tests where loose sand reservoirs saturated with viscous crude oils have been consolidated in the producing wellbore are presented and discussed, as are illustrations of the stimulated producing rates and descriptions of the equipment used in performing the sand consolidation. Based on results of the field tests, the details of a typical completion and the potential of the technique as a completion tool are analyzed.

Introduction

Sand control has been acknowledged as a producing problem in unconsolidated sand reservoirs for many years. As the viscosity of the produced crude increases, the sand control problem becomes more complex. In the early days of the development of shallow, unconsolidated sand reservoirs containing viscous crude oils, many of the oil operators contended that the sand should be produced with the oil. In early wells, provisions were made to bail both sand and oil from open-hole completions. Later, slotted liners with 0.18 to 0.20-in. openings were used which supported the wellbore but permitted the oil to carry sand into the well. Today, slotted liners, screens and gravel packs are the primary completion tools for wells producing viscous oil from unconsolidated sands. The only major change in California in recent years has been a general reduction of the slot size to 0.100 in. or less in an attempt to exclude the loose sand. Even though each of these mechanical methods has achieved some degree of success, each has inherent disadvantages. None of the mechanical devices affords permanent protection from recurring sand production. With mechanical devices in the wellbore, multiple completions are difficult. There are problem cases where mechanical devices have been completely unsatisfactory. The degree of selectivity is limited and interbedded water-bearing formations must be contended with in some producing areas. Several sand consolidation methods are presented in the literature. The diversity of approach emphasizes the fact that intensive research efforts have been directed toward the development of an effective sand control completion. Incentive for this research has been provided by several factors:

There is a need to maintain high productivity while controlling sand production. This is especially true in low gravity oil reservoirs that have not been developed because of sanding problems. A reduction of permeability can occur in some unconsolidated sands when they are permitted to move. If the unconsolidated sands contain interstitial clay, the reduction of permeability can be substantial since the clay particles become redistributed during movement. In these cases it would be desirable to consolidate the sand in the initial completion. Well and workover costs caused by sand influx could be eliminated. The recent development of thermal recovery processes with their greatly accelerated rates of production emphasized the immediate need for permanent sand control (as well as some degree of selectivity) before many of the unconsolidated reservoirs can be successfully depleted by secondary methods.

Thermal recovery processes have demonstrated their greatest application in viscous oil reservoirs which in turn present some of the most severe cases of sand control. This paper presents field test results of the warm air coking process. The potential of this method of sand consolidation in viscous oil sands has been demonstrated by stabilizing unconsolidated sand in several wells producing 12 and 14 degrees API gravity oil. In addition to consolidating the wellbores, the heat generated by the injected air has stimulated oil production for a limited period.

JPT

P. 35ˆ