Geologic and Dynamic Indicators Offering a Reliable Technology Paradigm to Reserve and Resource Estimation in Unconventional Oil Plays
Authors: Vassilellis George D. , Elrafie Emad A. 
Published: April 2016

Reserve and resource estimates and classification are meant to provide reasoned production expectations considering uncertainties and development risks. In conventional fields several estimation methods (volumetric, material balance, analogy, and production trends) can work in tandem in order to provide these reasoned estimates which relate to static and dynamic characterization. Despite intensive efforts to utilize all available data, these estimates could be still inaccurate, but have served our industry well in making business decisions.

With the introduction of the unconventional resources, this process requires re-examination and realignment to development priorities, risks, uncertainties and of course production drive mechanics. The early approach in recoverable volume estimation was based heavily on production trends and a statistical appraisal of observed variations with limited relation to production mechanisms and reservoir characteristics. Key work in many disciplines has shown that although production performance does not follow the same static and dynamic trends as in conventional reservoirs, it relates to certain static and dynamic subsurface characteristics particularly to natural fractures. Faults, fairway and background fractures become more important in liquid rich and oil plays (as fluids segregate) and invariably affect the process of hydraulic fracturing and the development of drainage patterns. Since natural fracture network characteristics may change rapidly even across the length of a horizontal well, it is difficult to expect a homogenous performance without the understanding of the natural fracture trends, reservoir characteristics and the change in the respective drive mechanisms. Most commonly used reserve and resource classification methods rely on proximity to existing production. Due to these effects, the expectation of similar performance in infill locations could be diminished. Apart from being an inaccurate prediction, this misconception may lead to the wrong development path in which wells classified as highest ranking may exhibit low performance. In the context of these observations it would be rational to draw fairway maps in relation to key geologic characteristics and dynamic effects utilizing all available information within and around the project area and to provide a basis for analogy which conforms better to the actual production drive mechanisms. In other words, using a physics based reliable technology (fairway maps) we are able to establish undeveloped areas with similar producibility at greater distances than production offset locations with reasonable certainty. Testing the validity of fairway maps with continuous development provides more confidence in predicting offset locations; classifying reserves and resources appropriately and guiding development towards better results. This process provides close alignment between development priorities and certainty levels in reserve and resource estimates which fulfills the basic requirements for rational project management. Subsequent application of fairway maps in other areas and similar plays may someday become a more general reliable technology paradigm for addressing unconventional resource assessment.