Significance of Partial Pressure Maintenance by Fluid Injection
Authors: Last G.J. , Craig F.F. , Reader P.J. 
Published: December 2007

Abstract
To investigate the feasibility of water flooding low capacity areas in the Pembina Cardium field, a calculation technique has been developed to predict the performance of a typical low capacity sand under a partial pressure-maintenance water flood. The calculation technique considers that the reservoir produces under a condition of continuous pressure decline, with a mechanism that is a combined depletion drive and water flood. As would be expected, the production performance under partial water flood is characterized by improved oil recovery, a declining reservoir pressure and an increasing GOR.Predictions for a typical low capacity Pembina property under a partial pressure-maintenance water flood are compared with the predicted performance of the same property under a partial pressure-maintenance gas injection scheme. It is concluded that in the Pembina field, the recovery under the partial pressure-maintenance water injection pro grain begun at the initial bubble-point pressure is approximately 15 per cent of the original oil in place, whereas recovery for the gas injection scheme is essentially the same. Both of these depletion schemes represent substantial recovery increases over the value of 9.5 per cent predicted for primary performance.
Introduction
Since discovery in 1953, the Pembina Cardium reservoir has been developed by drilling approximately 3,800 wells. The field now covers approximately 422,000 productive acres. Cumulative production from the Pembina Cardium pool to date is approximately 280 million bbl. The field produces in excess of 110,000 B/D, with pressure maintenance programs (the first initiated in 1956) contributing greatly to the steady production performance. Ultimate recovery for the field has been estimated in the vicinity of 2 billion bbl, with pressure maintenance being primarily responsible for an estimated 60 per cent of that recovery. For the most part, the full pressure-maintenance schemes in Pembina are in operation in the high quality-sand areas of the reservoir and are either five-spot or nine-spot water floods or 41-spot miscible floods. As these full pressure maintenance programs have been extended toward the edges of the reservoir, sand characteristics have gradually been less suited to this type of program. In particular, water injection capacity limitations have resulted in gas injection projects. It appears that partial pressure maintenance gas injection schemes are finding wide application in these low kh areas. Partial pressure maintenance by gas injection is the only partial pressure-maintenance fluid-injection method being used in Pembina at present. These programs have proven very well adapted to the lower capacity areas and the performance of these schemes continues to be attractive. The properties and performance of Pembina E lease, which are representative of the large area of the Pembina field characterized by low capacity sands, have previously been described. Fig. 1 depicts portions of the field that generally contain sands with less than 150 md-ft.
JPT
P. 20ˆ