Analytical Study Examines Production of Multistage Horizontal Wells in the Bakken

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 191455-18IHFT-MS, “Twelve Years and 12,000 Multistage Horizontal Wells in the Bakken: How Is Industry Continuing To Increase the Cumulative Production per Well?” by C. Mark Pearson, SPE, Larry G. Griffin, SPE, Stacy L. Strickland, SPE, and Paul M. Weddle, SPE, Liberty Resources, prepared for the 2018 SPE International Hydraulic Fracturing Technology Conference and Exhibition, Muscat, Oman, 16–18•October. The paper has not been peer reviewed. Multistage horizontal well designs were first implemented in the Bakken in 2007. Since then, more than 12,000 wells have been completed in either the Middle Bakken or Three Forks zones. Early-time production rates, as measured by 180-day state-reported cumulative production, have increased fourfold during this period, during which industry has pursued a program of innovation and continuous improvement in completions technology, with production per well increasing in 10 of 12 years. Through a big data analytical study comparing geological data, completions parameters, and state-reported production results, the authors have evaluated the fundamental changes that have guided industry to these production rates during the period discussed. Geology The Bakken Formation is Mississippian and Devonian in age and consists of Upper, Middle, and Lower members. The focus of this paper is to review work in both the Middle Bakken member and the lower Three Forks intervals contained within the Bakken Petroleum System. The Upper and Lower Bakken shales are the prolific source rocks for the petroleum system. The Middle member consists of distinct lithofacies that range from silty sandstone on the east flank of the basin to silty dolomite on the west flank. Porosities in the Middle member range from 4–10% and permeabilities are generally less than 0.1 md. Fig. 1 shows the basin depth structure map with a color fill of the thermal maturity of the Upper Bakken shale. The onset of oil generation occurred at a pyrolysis temperature (Tmax) of greater than 430°F as indicated in the figure by shades of green and warmer colors. Oil generation in this thermally mature window created overpressure and resulted in oil mobilization into less- mature and immature regions toward the extremities of the basin. The Bakken is a basin-centered system and thus the increased pore pressure that occurred with the process of kerogen conversion and the generation of oil has resulted in pore pressure gradients as high as 0.9•psi/ft in the deepest part of the basin. Unsurprisingly, in the deepest part of the basin, water cut is the lowest, with increasing water cut with distance from the areas of greatest thermal•maturity.• The complete paper provides a detailed description of the Bakken development history, which the authors divide into seven periods beginning with first production in 1953 to the present. Production Bakken production has grown historically, but as recently as early 2004 it yielded only approximately 25,000 BOPD. The increase in drilling activity then drove production growth, with an initial peak in December 2014 of 1.22 million BOPD. The rapid decline in industry activity then resulted in a significant production drop. However, the decline reversed, and new production records of 1.23 and 1.24 million BOPD were set in June and July of 2018. The return to peak production levels has been driven by companies using more-effective•completions.