Integrated Reservoir Fracturing And Completion Study To Maximize Productivity Of Individual Niobrara Wells In Yuma County, Colorado
Authors: Blauer R.E. , Brady B.D. , Holcomb D.L. , Robinson F.L. 
Published: December 2007

Consistently and continuously applied fracturing, reservoir and production engineering used to increase recovery from a marginal production low-permeability and low-pressure dry-gas reservoir has approximately doubled the initial production rate and the estimated ultimate recovery expected from new wells. The on-going costs of the additional engineering and technology to sustain the increased productivity of this reservoir is a few cents per MCF. As a result, new, wells can be drilled and produced economically, the selection criteria for acceptable infill and exploration locations is greatly expanded, and proven gas reserves for both the new wells and the region are increased. Significant performance improvement can be achieved using a minimum number of wells, consistently collected data, and continuous review of performance changes caused by completion procedures changes. Exploitation optimization is an evolutionary process, not a one time study.

Introduction

The Niobrara Chalk Reservoir located in Eastern Colorado and Western Kansas was originally discovered in 1912, but was not commercially developed until the mid-1970's when a combination of increased gas prices, tight-gas tax incentives and improved fracturing technology permitted economic completion of the low-pressure dry-gas reservoir. During the gas price peaks in the early 1980's the reservoir was extensively drilled because the probability of a non-economic well located in an offset or extension location was low, drilling, completing and operating costs were low, and profitability was reasonable. However, the enthusiasm to drill waned as gas prices fell and producing economics of wells became marginal.

Typically, operators with similar, marginally-economic, reservoirs are reluctant to apply and use the currently available technology due to the additional procedures required to obtain data, the costs of obtaining and analyzing the data, additional complications with logistics to complete wells, the requirements to continue well monitoring and the possibility that well completion and operating costs will increase without enjoying a significant increase in either productivity or ultimate recovery. Consequently, optimization studies of low-productivity reservoirs are often conducted which focus on only one aspect of a drilling, completion, or production program. This type of optimization study may reduce costs connected to the particular aspect examined, but may increase costs in another. Further, such optimization studies are conducted with little attention paid to expected ultimate recovery since economic rate-of-return is most readily affected by cost reductions during the first year of production. Exploitation optimization, especially in marginal reservoirs, requires attention to both cost and recovery.

Two operators with producing wells completed in the Niobrara Chalk determined their needs required a full, integrated geologic and reservoir study to maximize the value of the reserves from this reservoir. The goals of the on-going study are both to increase the proven reserve potential for several hundred in-fill and step-out locations in existing fields and to determine the best locations for exploratory wells in newly acquired acreage. The results to date include approximately doubling initial production rates and ultimate recovery from new wells, increasing productivity of certain existing wells, significantly reducing the number of marginal producing wells, and providing selection criteria for exploratory locations which has essentially eliminated dry-holes.

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