Core Analysis Study for the El Dorado Micellar-Polymer Project
Authors: Pusch W.H. 
Published: December 2007

Introduction

The marginal economics controlling improved recovery processes in watered-out reservoirs have placed processes in watered-out reservoirs have placed increased emphasis on reservoir engineering and cost optimization. A detailed knowledge of reservoir properties has become essential. For the El Dorado field micellar-polymer project, 31 wells were cored within a 52-acre area. Even with the data generated from such a high well density, it has been difficult to predict reservoir properties and formulate a satisfactory field-wide model. properties and formulate a satisfactory field-wide model. Information obtained from routine core analysis proved invaluable in the process design phases and should be helpful in explaining project performance.

The two primary objectives of the El Dorado micellar-polymer coring program were to acquire a detailed description of the reservoir and to obtain formation samples for laboratory testing. Reservoir parameters sought were porosity, oil saturation, and permeability, and their distribution over the project area. Knowledge of localized anomalies would be useful in explaining possible differences in well behavior that could affect over-all possible differences in well behavior that could affect over-all project performance. Formation samples are necessary to project performance. Formation samples are necessary to determine the mineralogical and strength characteristics of the reservoir rock. Laboratory flow tests using El Dorado cores are needed to study adsorption, fluid mobilities, and oil recovery for design of the micellar-polymer process. In addition, preserved samples of the reservoir as it exists before the chemical flood might prove useful as the state of the art improves. prove useful as the state of the art improves. Coring Procedures

Fig. 1 shows the pattern configuration and types of cores for the demonstration project. Two factors considered in the coring operations were residual oil saturation and rock wettability. Although it was generally conceded that oil present in the cores would be flushed to residual, one of the five test wells was cored with a low-fluid-loss emulsion mud to inhibit filtrate penetration into the core. The mud contained 10-lb/bb] pregelatinized starch, 8-lb/bbl bentonite, and small amounts of caustic soda, biocide, and soda ash. The drilling fluid for all other wells was El Dorado produced water. To preserve native formation wettability, which often is thought to be altered during coring, eight cores were cut with deaerated brine containing oxygen scavenger (0.25-lb/bbl sodium sulfite). These cores were wrapped and sealed at the wellsite to minimize contact with the atmosphere and possible alteration of rock and fluid properties.

Core Analyses

Twenty-five cores from the project area have been analyzed to determine local reservoir porosity, permeability, pay thickness, and immobile oil saturation. permeability, pay thickness, and immobile oil saturation. The laboratory methods used for the analyses are defined in Ref. 1. Data were measured at 1 -ft intervals corresponding to the footages marked on the core. This sampling procedure is thought to be unbiased and over the large procedure is thought to be unbiased and over the large number of points analyzed, the measurements should yield a fair representation of kh, the flow capacity, of the formation.

Discussion of Results Porosity and Oil Saturation Porosity and Oil Saturation JPT

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