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Hydraulic-Fracture Design: Optimization Under Uncertainty

Fig. 1—Probability distribution of nonproductive time. Nstage=number of fracturing stages.

Massive hydraulic fracturing is a costly operation, particularly offshore where logistic constraints and high rig rates add significant financial risk. For the Lower Tertiary Gulf of Mexico, limited production from analogous fields and very high appraisal-drilling costs result in huge uncertainty for key reservoir parameters and a lack of consensus on best practices for fracture design. This paper provides new approaches to fracture design for thick, vertically anisotropic reservoirs, when considerable uncertainty in reservoir parameters amplifies the financial risks associated with water depth and remoteness.

Risk Analysis

Offshore applications are subject to significant risk because of hostile operating environments and the extreme costs involved. Although multistage hydraulic fracturing for productivity is common onshore, with financial risks well understood, the same cannot be said for offshore.

Compared with the entire cost of drilling and completing an offshore well, the proppant cost is nearly insignificant. However, the risk associated with fracturing is paramount because any nonproductive time could cost millions of dollars because of high day-rate costs.
For future analysis and forecasting, a Markov chain of completion time with respect to number of stages was generated. The Markov chain represents an independent transition from one state to the next. The transition does not depend on the previous states, only on the current state. Assuming a log-normal distribution, a series of Markov chains is generated to predict nonproductive time associated with fracturing additional stages.

This article, written by Special Publications Editor Adam Wilson, contains highlights of paper OTC 25179, “Hydraulic-Fracture Design for the Lower Tertiary Gulf of Mexico: Optimization Under Uncertainty,” by S.B. Podhoretz, SPE, and P.P. Valkó, SPE, Texas A&M University, prepared for the 2014 Offshore Technology Conference, Houston, 5–8 May. The paper has not been peer reviewed.
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Hydraulic-Fracture Design: Optimization Under Uncertainty

01 March 2015

Volume: 67 | Issue: 3

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