Infill-Drilling Potential in Tight Gas Reservoirs

[+] Author and Article Information
Shu Luo

e-mail: shu-luo@utulsa.edu

Mohan Kelkar

e-mail: mohan@utulsa.edu
McDougall School of Petroleum Engineering,
The University of Tulsa,
800 South Tucker Drive,
Tulsa, OK 74104

Contributed by the Petroleum Division of ASME for publication in the Journal of Energy Resources Technology. Manuscript received April 23, 2012; final manuscript received July 26, 2012; published online November 6, 2012. Assoc. Editor: W. David Constant.

J. Energy Resour. Technol 135(1), 013401 (Nov 06, 2012) (8 pages) Paper No: JERT-12-1083; doi: 10.1115/1.4007662 History: Received April 23, 2012; Revised July 26, 2012

Many operators of tight gas reservoir fields are interested in determining the infill well potential in these fields. Over drilling may prove to be uneconomical; whereas, under drilling would leave unexplored reserves under the ground. In predicting EUR (expected ultimate recovery) of a potential infill well, operators are interested in knowing what percentage of the production will be come from incremental reserves (newly accessed) and what percentage is from acceleration reserves (which can be produced from existing wells). So, higher the percentage of incremental reserves better is the potential of an infill well. In this paper, we present a novel method for determining the incremental versus acceleration potential for infill well in a tight gas reservoir. We evaluate the existing wells by plotting the data in a form so that the data can be linearly extrapolated. Then, we can predict the EUR for individual wells before and after new wells in the vicinity are drilled. By knowing how much gas is “diverted” from the older wells, we determine the acceleration component of an infill well. By repeating the process as the field is being developed, we can determine the fraction of acceleration and incremental components of the EUR at each stage of infill drilling. We will also know how the EUR is changing as the well spacing is slowly reduced. To ensure our results are reasonable, we also compare our EUR values with EUR’s reported by the operator as proved reserves. Armed with this information, we can extrapolate infill well potential for a smaller spacing, including the contribution due to acceleration versus incremental production. We applied this procedure for Wamsutter field in Wyoming. Using the procedure, we recommended infill well locations to the operator. Operator has drilled seven wells based on our recommendations. Using this new method, we can predict the EUR for infill well as well as acceleration and incremental contribution of the infill well. Thus, potential of infill wells at different locations can be evaluated and compared.

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Fig. 1

Homogeneous reservoir and production of five wells

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Fig. 2

Heterogeneous reservoir and production of five wells

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Fig. 5

Southwestern energy gas type curve

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Fig. 6

Chesapeake gas type curve

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Fig. 7

Southwestern energy gas type curve plot versus t0.5

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Fig. 8

Chesapeake gas type curve plot versus t0.5

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Fig. 9

Area map of well locations in study area

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Fig. 11

Grouping of wells based on chronological sequence

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Fig. 12

Acceleration production

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Fig. 13

EUR comparison between operator values and our method

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Fig. 14

Acceleration versus incremental plot

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Fig. 15

Extrapolation to lower spacing




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