8/12/2019 spe159597-page1

1/1

SPE 159597

Mini-DST to Characterize Formation Deliverability in the BakkenKurtoglu, B., Marathon Oil Company, Kazemi, H., Colorado School of Mines, Boratko, E.C., Tucker, J.,Schlumberger, and Daniels, R., Marathon Oil Company

Copyright 2012, Society of Petroleum Engineers

This paper was prepared for presentation at the SPE Annual Technical Conference and Exhibition held in San Antonio, Texas, USA, 8-10 October 2012.

This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not beenreviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, itsofficers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission toreproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright.

Abst ract

Characterization of reservoir deliverabilityis fundamental for the economic development of any field. In the Bakken, there is aneed for reliable pressure transient tests to provide the effective formation permeability of the fracture-matrix in this formationfor deliverability calculations. This effective permeability can then be compared to laboratory measured core permeability ofthe matrix rock samples. This comparison is the basis for planning early production options and subsequent enhanced oilrecovery (EOR) decisions. This comparison is particularly important because of the influence of massive hydraulic fracture

stimulation on reservoir performance.

Determining well deliverability potential by conventional drill stem tests (DST) or traditional wireline formation tests (WFT)in the past has resulted in mixed success in the Bakken. On the other hand, the mini-DST has definitely increased reliabilityand the success rate of pressure transient tests. The operation of mini-DST tool requires much less time than the classic DST,and multiple zone tests can be conducted to assess individual zone deliverability. The Mini-DST tool uses the conventionalWireline Formation Tester (WFT) configured with a dual-packer module and downhole pump. Tests are conducted byinflating the dual-packer module to isolate a 3-foot interval of the wellbore. The formation fluid is pumped out from thepacker-isolated wellbore interval to conduct pressure drawdown and buildup tests in the interval. An overlay of all thepressure drawdown and buildup results from various intervals is compared on a single plot to identify the most productive

interval. Finally, conventional pressure transient analyses are performed to interpret all pressure drawdown and buildup tests.In this paper we present several field tests which were analyzed both by the above procedure as well as by numericalsimulation.

The analyses of several mini-DST results have provided insight into a better understanding of the flow mechanism in theBakken both during primary production and in forecasting various improved and enhanced oil recovery proposals. Theexperience can also serve as a basis for test design in similar low-permeability reservoirs elsewhere.

Introduction

The Williston Basin is a large sedimentary basin that covers parts of North Dakota, Montana, South Dakota, Saskatchewan,and Manitoba (Fig. 1). The Bakken formation, regionally in the Williston Basin, is comprised of upper and lower organic-richblack shale and a middle silty dolostone or dolomitic siltstone and sandstone member (Fig. 2). The Bakken is overlain by theLodgepole formation which consists of a dense, dark gray to brownish gray limestone and a gray calcareous shale andunderlain by the Three Forks formation which is composed of thinly interbedded greenish gray and reddish brown shale, light

brown to yellow gray dolostone, gray to brown siltstone, quartzite sandstone and minor occurrences of anhydrite (Kume,1963). The Upper and Lower Bakken shale are the potential petroleum source rocks for both the Bakken and Three Forks

Formations. Depositional environments for the Bakken formation range from a marine swamp with restricted circulationcaused by the prolific growth of organic matter to an offshore marine environment with a stratified water column (LeFever,1991).