Demulsifier Squeeze Treatments Elk Basin Embar Tensleep Reservoir
Authors: Reese David D. 
Published: December 2007

Emulsions, both naturally occurring and induced, create difficult production obstacles in Elk Basin Embar - Tensleep reservoir. As pressure drops in this low pressured gravity pressure drops in this low pressured gravity drainage reservoir, emulsion problems intensify.

Demulsifier squeeze treatments, however, have generated outstanding results in combatting these problems. They have replaced toluene and acid treatments, reducing average treatment costs from $15,000 to $2,500. Initial production increases from these treatments of 50% to 200% result in payouts ranging from 1–2 weeks. payouts ranging from 1–2 weeks. The basic treatment consists of pumping 500 barrels gasoline, condensate or crude, that has been blended with 1% demulsifier, into the formation and flushing with 250 barrels to 1000 barrels of crude. This type of treatment has increased production from wells producing water-oil emulsions and has also restored production to wells that have experienced production drops following workovers.

The production increases typically last from one to six months. Some wells have had more than one treatment, allowing comparison to be made between different types of treatments.

Introduction

In recent years, numerous wells in Elk Basin Embar Tensleep have experienced severe production declines. Obvious changes in reservoir conditions were known to be the problem on many occasions but there were other times when no apparent reason could be found. A new type of treatment for this reservoir characterized as a "demulsifier squeeze" has shown remarkable success in restoring and increasing production from these wells. Initial production increases of 50 to 200% are regularly observed. Although many of these production increases decline within a month, they decline production increases decline within a month, they decline to a production rate that is significantly higher than pretreatment rates. This paper describes these treatments and successes.

Reservoir Conditions

Elk Basin Embar - Tensleep is located in the Big Horn Basin of northwestern Wyoming at an average depth of 5,000' (see Figure 1). This is a gravity drainage structure that consists of the Embar dolomite commingled with the Tensleep sandstone. Pertinent reservoir data is included in Table 1. Reservoir pressure was maintained through solution gas and inert gas injection until the expansion of the gas cap made further gas injection uneconomical. Secondary recovery through waterflooding was tried and abandoned after the rapid breakthrough of injected water at offset producers. producers. Current production comes from an oil ring between a large low pressured gas cap and a relatively inactive water zone (see Figure 2). During the last 18 months, the gas cap pressure has dropped from 330 psi to 250 psi. Production is currently 7000 BOPD and 3500 BWPD with a GOR of 2800. The cumulative recovery is 61% of the original 510 MMBO in place.

Emulsion Problems

A natural water-oil emulsion is produced from this reservoir. In past times when reservoir pressure was high and the percentage of emulsion pressure was high and the percentage of emulsion was low, there was little production difficulty. But, as the field was depleted, the percentage of emulsion increased and the pressure decreased. In certain areas where the emulsion is prevalent, the reservoir fluids are reluctant to flow.