Abstract

Poor well performance due to permeability and conductivity damage can often be attributed to unbroken gel residue or inadequately reduced filtercake on formation faces. These forms of polymeric damage can negatively impact production rates by restricting the flow of oil or gas from the formation. Remedial treatments have been applied to wells exhibiting this type of damage using acids, oxidizers and enzymes. These removal treatments, when applied to accurately diagnosed polymer damaged wells and effective breaker systems are utilized, have shown to increase well production dramatically. However, polymer damage is only one of many factors that might be responsible for impeding optimum hydrocarbon flow. Therefore, the key to the success of a removal treatment is proper evaluation for polymeric damage when selecting a treatment candidate.

An improved flow back analysis has been recently introduced as a series of tests for polymer damage and for the evaluation of treatment load recovery. The testing procedures involved in that analysis can also be applied in candidate selection for remedial treatments and for monitoring the resulting clean up progress. Samples are analyzed before and after the treatment to determine total carbohydrate content, molecular weight distributions and the standard pH and viscosity measurements. The utilization of this improved analysis can assist in the selection of appropriate candidates and further direct treatment design. Several case histories on low performance wells are presented and include laboratory data to demonstrate candidate selection. Treatments with enzymes were used and detailed results are provided to evaluate the amount of polymer recovered. This paper also presents a guideline for use in the selection of candidates for remedial treatments.

Introduction

Polymers are frequently employed within this industry for drilling, completion and stimulation operations. The polymers used are selected based upon their ability to provide viscosification, proppant transport and/or suspension, fluid loss control and zonal isolation. Yet the very properties for which they are chosen also make them difficult to break down following their application. Unbroken filtercake and insoluble high molecular weight polymer fragments are just two forms of damage produced by polymers. It is these residual effects of polymers that are responsible for reducing productivity through damage to a formation's permeability and conductivity. Hydraulic fracturing is one application through which significant polymer damage can occur. Treatments usually require gel systems utilizing high polymer loadings, yielding tremendous viscosity, in order to propagate the fracture and transport proppant there. Due to the effects of fracturing treatments, such as fluid leak-off and fracture volume reduction upon closure, the polymer becomes concentrated on the formation faces and within the proppant pack. At times the concentration of this polymeric filtercake becomes so high that breaker additives are no longer able to thoroughly degrade it. The goal then becomes the reduction or removal of the polymer damage in order to obtain optimum productivity in the most cost-effective manner.

Remedial treatments designed to remove polymer damage from existing fractures in effort to increase productivity have been in use for many years. Different breaker technologies have been incorporated into remedial techniques to remove residual polymer damage. Historically, strong acids or oxidative breakers were utilized to degrade the polymer. Recently, the application of enzymes in polymer damage removal treatments have resulted in multifold well productivity improvements. Unfortunately, there are many factors which might also be responsible for the reduction of a well's productivity. Organic deposition, fines migration, water production and scale are a few examples of other problems which could affect production rates. The effectiveness of a removal treatment will not be realized if the primary impairment to the well production is anything other than insufficiently degraded polymer. P. 59^

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