Resolution of the Principal Formation Damage Mechanisms Causing Injectivity and Productivity Impairment in the Pembina Cardium Reservoir
Authors: King R.W. , Adegbesan K.O. 
Published: December 2007

Abstract
The Pembina Cardium reservoir is the largest conventional oil reservoir in Canada, containing 1.1 × 10 9 m3 of original oil-in-place. The main recovery operation is water flooding. Field observations and reservoir analyses confirm that in situ wax precipitation and particulate deposition impair both injectivity and productivity in this pool.
Work to resolve the contributions of several damage mechanisms involved laboratory experimentation and reservoir engineering analysis. Phase equilibrium studies determined the conditions necessary for wax deposition in the reservoir. Coreflood studies characterised the wax deposition behaviour and the resulting permeability reduction. Reservoir engineering analysis included the development and application of analytical and numerical simulation models to describe wax/particle transport and deposition in the reservoir to explain observed field performance.
This investigation has resulted in new analytic methods not previously reported in the technical literature:laboratory and reservoir analysis techniques to identify formation damage mechanisms affecting productivity and injectivity and to measure relevant parameters to quantify damage;phase envelope for wax deposition using reservoir fluids;injectivity analysis of field injection wells and quantification of the reduction of injectivity resulting from fill-up, fluid displacement and formation damage;description and performance of analytical formation damage models in fitting observed field injectivity data;incorporation of key formation damage mechanisms in reservoir simulation models to enable history matching of field performance.

Introduction
In late 1993, the major operators in the Pembina Cardium field, with support from their affiliates, began a collaborative effort to determine how to improve performance and recovery for the pool. This paper focuses on part of the efforts to understand the principal causes of formation damage in pool.
The Pembina Cardium Field in west-central Alberta was discovered in 1953 and waterflooding has been the principal recovery method since 1960. in most production wells, a steady decline is seen in both oil and total fluid rates. Injection wells require increased pressure to maintain injection volume targets, or else experience reduced injection volumes. Formation damage is a probable cause for these behaviours. Older studies by various operators concluded that while clay swelling and fines migration do occur in parts of the field, these cannot explain field performance. Indeed, numerical simulations have used declining well indices to achieve history matches, but no specific physical justification was identified.
Anecdotal field data shows the major operational problems in the field are paraffin deposition, fines migration, corrosion, scale, and bacteria. The purpose of this study was to investigate the principal causes, locations, and magnitudes of formation damage.

Field Observations
Wax Deposition. Wax deposition in production well tubulars is the most significant operational problem encountered in the Pembina Cardium Field. This problem is endemic to production wells and it is becoming harder to clean up. Historically wax has been removed by hot oiling the wells; however, operators have switched to other wax removal methods, including strong solvents, chemicals, and microbes. The use of scrapered rods in the wells is now common practice. P. 277