Saturation modeling in a carbonate reservoir using capillary pressure based saturation height function: a case study of the Svk reservoir in the Y Field

P Q Lian,C Y Ma,X Q Tan,R Q Feng,H M Gao

doi:10.1007/s13202-015-0159-9

Abstract

Because of the complex pore structure and the strong heterogeneity of the Svk carbonate reservoir in the Y Field, water saturation distribution and petrophysical properties, such as porosity, permeability and capillary pressure are difficult to be characterized. To solve this problem, a new method to interpret water saturation was presented. By this method, the relationships among porosity, permeability and different pore throat radii are fitted and a typical radius R30 (the pore aperture radius corresponding to 30 % of mercury saturation in a mercury penetration test) selected. By fitting the capillary pressure curves with Corey–Brooks function, the threshold pressure, the irreducible water saturation and the Corey exponent “n” of each capillary pressure curve can be determined, and the relationship between R30 and the threshold pressure, R30 and the irreducible water saturation, and R30 and the Corey exponent can all be fitted. If the R30 value is known, the threshold pressure, irreducible water saturation and Corey exponent can be calculated by the fitting equations; hence, the water saturation at a given height from FWL can be calculated by the Corey–Brooks function. The water saturation calculated by saturation height function is consistent with that of the well log interpretation and the error is less than by other methods. During the process of three-dimensional saturation modeling, an R30 criterion is presented to define rock types, six petrophysical rock types with different reservoir properties are distinguished and a link is set up between rock types and log responses by the KNN method. Logs are utilized to predict rock types of non-cored wells according to this link, and a three-dimensional rock-type model is established by the Petrel software. R30 value of each grid can be calculated by R30 formula when three-dimensional porosity and permeability models are built with the restraint of rock-type model. Then, on the basis of the saturation height function, a three-dimensional water saturation model can be obtained.

Highlights

Confirming the saturation distribution of a geologic model is a key step in the process of OOIP calculation of any integrated reservoir
If the R30 value is known, the threshold pressure, irreducible water saturation and Corey exponent can be calculated by the fitting equations; the water saturation at a given height from FWL can be calculated by the Corey–Brooks function
Saturation distribution of a geologic model is very important for OOIP calculation of reservoirs

Summary

Introduction

Confirming the saturation distribution of a geologic model is a key step in the process of OOIP calculation of any integrated reservoir. To interpret the water saturation more accurately, a new method has been presented to obtain a good match for complex carbonate reservoirs In this method, typical radius R30 (the pore aperture radius corresponding to 30 % of mercury saturation in a mercury penetration test) is selected to describe the flow capacity of carbonates, and capillary pressure curves are used to establish the saturation height function by combining Corey–Brooks function and R30. Winland used the mercury injection–capillary pressure curves to develop an empirical relationship among the porosity, the permeability and the pore throat radius of the reservoir rock obtained from Spindle Field, Colorado. After all capillary curves from core samples have been smoothed and fitted by the Corey–Brooks function, a set of Corey parameters, i.e., the threshold pressure, the irreducible water saturation and the Corey exponent, can be derived. Ð8Þ nÀ1 where subscripts (log) and (core) denote the values obtained from log and core analyses, respectively

Methods

Findings

Conclusions