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© 2020 GEORGE VASSILELLIS PLLC

© 2020 GEORGE VASSILELLIS PLLC

Innovation Design

The horizontal well design with transverse fractures was originally incepted for gas formations that exhibit simple drive mechanisms. Following the successful shale gas revolution the late part of last decade, the adaptation of this design in liquid rich and oil bearing formations seemed to work also in making economic wells. At that point the oil price being beyond handsomely rewarding, any signs of design flaws or inefficiencies were brushed aside in favor of keeping up with the pace of development.
With the establishment of Repsol’s technology hub in early 2013 at The Woodlands, TX, we had the opportunity and the influence to deploy significant resources to the field with the objective of redesigning a challenging tight oil play with high water cut and very “spotty” performance. In that we coordinated the activities of Repsol’s research center in Madrid and we used the outcome of several related long-term research projects. The rich geological, geomechanical, geophysical and surveillance data provided a link between the regional oil generation scale to the completion level while we had the ability to use sophisticated data mining and modeling tools. The outcome of this effort was the discovery of particular geological drivers and the design of a new oil extraction system, which was capable to extract more oil at less cost and less variation in performance.The new system is designed to address the complex drive mechanisms in tight oil plays, which include compaction and gravity segregation. The shearing and the reactivation of natural fractures create the need for a simple but yet functional design employing stimulated and un-stimulated laterals which can be combined in multilateral wells simplifying the artificial lift challenges and costs. As a result it was demonstrated in the field that this design could produce 40% more oil at lower water cut at almost half the CAPEX and half the OPEX of previous operations.
The shale engineering models were particularly successful in optimizing the design concept and in offering an accurate prognosis, which was only 10% lower than the actual IP. Before the outcome of this field experiment had reached a year of maturity, the operator had already undertaken the initiative to drill more than 40 multilateral wells, influencing the up to that point unfavorable play metrics in the face of the severe oil price drop in 2015. The water disposal challenges with associated earthquakes and the start of bankruptcy proceedings in 2016 imposed a slowing down in the development, but as I understand it is slowly getting back on track. The leanings of this effort are applicable to other tight oil plays and the new well design which differs from the typical shale gas configuration in terms of lateral well placement and stimulation intensity and I believe that in time would become the oil extraction standard for unconventional plays. Several operators have already started making adaptations to multilateral wells having in mind cost savings and operational simplification and I will be reasonably evident that the reservoir drive benefits could add a much more significant element of higher oil recovery and extraction cost reduction if they are properly engineered.

George Vassilellis, Emad A. Elrafie, S. Duffy Russell, Jack Austin, and Chet Ozgen.  2015. “The Role of Drive Mechanisms in Redesigning Development Practices in a Fractured Tight Oil Carbonate Resource,” SPE 2154951, Unconventional Resources Conference USA, San Antonio, 20-22 July.

My position was senior technical advisor reporting to the upstream director of the Center of Research and Development in Madrid. A a co-founder of the hub, I was responsible for managing the tight oil project, including contracting, budgeting as well as offering technical guidance.
Austin, J., Elrafie, E., Vassilellis, G., Russell, D., Howle, T., Rodriguez, A., de Grood, R., McCarty, R., and Gil, J. 2015. “Innovation in Well Design and Lifting Coupled with Subsurface Understanding Provides New Development Concepts in a Tight Oil Carbonate Resource,” SPE 2154888, Unconventional Resources Conference USA, San Antonio, 20-22 July.
George Vassilellis, Emad A. Elrafie, and Chet Ozgen. “Including Hydro-shear in a Practical Reservoir Simulation Model to Improve Well Design in a Fractured Tight Oil Carbonate Resource”. 2016. AAPG 2383169, Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016