Abstract

Mercury injection capillary pressure (MICP) analyses applied to modelling reservoir rock pore systems was popularized a little more than a decade ago. However, MICP analyses are time consuming and there is a need to utilize existing MICP databases to determine the pore geometry parameters for unanalyzed reservoir rocks.

Recent studies have demonstrated that pore throat sorting and displacement pressure are two MICP parameters that may be used to characterize reservoir pore systems. These two parameters can be quantified by one value, R35, the pore throat size at 35% mercury saturation in an MICP analysis. The relationship between R35 and porosity and permeability may be determined using multiple regression, making data from core analyses a useful means of quantifying pore geometry in a reservoir interval and graphs of R35 vs core analyses depths can be used to characterize pore geometry variations in those intervals.

Two hundred and thirty jive MICP analyses from reservoir studies in Saskatchewan make an excellent database to characterize the pore geometry a reservoir and non-reservoir rocks using R35/depth plots. The combination of these plots and detailed lithologic studies, including facies and diagenetic analyses, promote a better understanding of the factors influencing reservoir quality in some Middle Devonian Winnipegosis and Mississippian Frobisher and Midale reservoirs.

Introduction

The implementation of enhanced recovery techniques to improve reservoir productivity mitigates that the geology of the reservoir rocks, is well understood. Two elements of the geology, lithotypes and diagenesis, can significantly influence reservoir pore geometry, and thus reservoir quality. Pore geometry can be characterized using components of mercury injection capillary pressure analyses (MICP), particularly uniformity of pore throat sizes and displacement pressure (entry pressure).

Mercury injection capillary pressure analyses have been an integral part of carbonate rock hydrocarbon reservoir studies carried out by graduate students and faculty of the Department of Geology, University of Regina, during the past 16 years. From the beginning, it was anticipated that by including this procedure in the reservoir studies, it would helped, firstly, to develop a better understanding of the geometry of an assortment of pore networks in carbonate reservoir rocks; and secondly, it would establish a database of MICP components that in the future might be employed. in some way, in the evaluation other carbonate reservoirs.

The intent of this paper is to employ an empirical method based on an existing MlCP database Lo characterize carbonate reservoir pore networks, using core analyses data. The database consists of 230 MICP analyses from studies done at the University of Regina on carbonate reservoirs from the Mississippian of southeastern Saskatchewan. The empirical procedure in this study is applied to reservoir rocks from three stratigraphic levels: the Middle Devonian Winnipegosis in the Tableland-Hitchock-Macoun area, and Mississippian Frobisher and Midale Beds in the South Workman Pool and the North Tatagwa area, respectively.

Background to MICP Analyses

Figure I demonstrates the basic elements of an MICP analysis and the principles are listed below:

I) - MICP analyses are conducted on core-plugs, 20cm in diameter by 40cm long.

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