How Close is too Close? Well Spacing Decisions Come With Risks

Abstract

There is no formula for properly spacing wells in unconventional plays. When a reservoir consultant recently described conversations with clients about how many wells they could drill per acre, it sounded like a doctor advising a patient considering back surgery. “I am not trying to tell you what your spacing should be,” said Miles Palke, management senior vice president for Ryder Scott, adding that the modeling and production history matching his company offers is “a process to help you inform your decision.” The cautious approach was understandable in his talk at the recent SPE Hydrocarbon Economics and Evaluation Symposium. Well-spacing decisions are increasingly tricky because of the potential downsides, from damaging hits to older parent wells to production from new child wells falling short of the old wells. A recent technical paper authored by Schlumberger (SPE 191799), based on data from the Wolfcamp shale play in the Permian’s Delaware Basin, found that when a new well is drilled within 1,000 ft of an older well, the older parent well outperformed the child well 66% of the time. When the results were adjusted for the bigger, more expensive completions now common, 79% of the older wells performed better. It is getting harder to avoid the issue of well spacing. In its recent earnings call with investment analysts, Schlumberger said that 70% of the wells drilled in the Eagle Ford are infill wells, as are 50% of those wells drilled in the Permian. While there is a lot of agonizing about fracs hits when wells are closely spaced, wider spacing also has its risks. Schlumberger predicted that even when the wells are 2,000–2,500 ft apart, the parent wells perform better 61% of the time when the production was adjusted for the larger volumes of proppant per foot now commonly used. As wells get farther apart, there is a growing chance that productive rock in between will never be stimulated. Well interactions are a constant reminder that fracturing does not create networks of producing fractures shaped like shoe boxes that can be lined up neatly on a shelf. Fracturing the maximum volume of a reservoir requires dealing with the contact that comes when wells with irregularly shaped fracture networks are located side by side. “People talk about well interference and bring it up as if it is a bad thing,” said Erdal Ozkan, SPE’s reservoir technical director. The petroleum engineering professor at Colorado School of Mines added that overlapping production “has always existed between two wells in the same field. There will be interference. If you reduce the drainable area, you reduce productivity of each well.”