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How to evaluate shale oil recovery, reserves?

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How to evaluate shale oil recovery, reserves?

Jinxiu Qi

Calgary AB, Canada Jinxiu Qi Posts: 1

Can decline curve be used to evaluate shale oil recovery? Does it depends on fractures created during completion? What is the major driving mechanism? Solution gas drive or natural depletion? The reservoir is Duvernary formation which is about 2800m in depth, oil API 48. Thanks! 

RE: How to evaluate shale oil recovery, reserves?

John Belgrave

Calgary Alberta, Canada John Belgrave Posts: 121

Hi Jinxiu,

What follows are two useful complimentary empirical tools for evaluating tight oil and shale gas.

Decline Analysis

Although there is not much information available at this time on mature tight oil and shale gas plays, decline curve analysis apears to be a useful tool if it is recognized that the low reservoir hydraulic
diffusivity can result in two decline regimes.

Initially the drainage area surrounding the well will behave like an open system as the depleted area slowly expands. This period can be lengthy and the associated decline will be hyperbolic (decreasing decline rate year over year). Later, when well interference and/or boundary effects are experienced, the drainage area will behave like a closed system and the decline will be exponential (constant decline rate year over year).

This means that dependence on "early-time" decline data could lead to an erroneously high reserves estimate.

Power Law Relation between Reserves and Producing Potential

There is an established power law relationship between reserves and producing potential (rate).

Tight oil reservoirs appear to follow the same trend as conventional oil reservoirs. This is in contrast to shale gas and conventional gas which do not follow a common trend.

In the case of oil, the power law relationship (see reference) is:
          Qpeak = 0.26 * K0.7088
where Qpeak is in million barrels per day, and K is the size of the reserves in in billions of barrels.

The relationship for gas shale plays is:
          Qpeak = 0.23 * K1.0664
where Qpeak is in billion cubic feet per day, and K is the size of the reserves in trillion cubic feet.
The equivalent relationship for conventional gas fields is:
          Qpeak = 0.087 * K1.0664

Reference

Rafeal Sandrea: "Evaluating production potential of mature US oil, gas shale plays", Dec. 2012, http://www.ogj.com/articles/print/vol-110/issue-12/exploration-development/evaluating-production-potential-of-mature-us-oil.html

Post updated at Friday 7th of June 2013 2:48:46 PM.

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