Fracture Stimulate and Effectively Prop Fracs: The Conductivity Challenges of Liquids Production from Ultralow-Permeability Formations

摘要

A proliferation of massive new resource rock (shale) gas fields has come on-stream in the past several years. This has significantly increased gas production and, along with an economic slowdown globally, these factors have combined to create a gas glut in North America and a corresponding fall of gas prices. The industry response to these very low prices has been to reduce the number of rigs drilling for gas; many have been redeployed to several promising new (or reinvented) liquids producing "shale" fields, including gas shales making condensate, as well as traditional very low permeability oil formations. The development of a new completion approach quickly transformed the low-permeability sector of gas and oil well completions—drill a long (flat and straight) lateral section through the heart of the reservoir and then complete with transverse hydraulic fracture stimulations at several points along the lateral, just as if each point (perforation set) were an independent vertical well location (i.e., the Shale Completion Model). The industry also adopted as its primary horizontal completion technique a process called "perf-and-plug," in which pumpdown plugs are used with attached multifire perforating guns. At least three and often up to seven separate intervals are perforated and simultaneously fracture stimulated, adding potential challenges to effectively place proppant into all fractures and achieve or maintain near-wellbore (NWB) conductivity. Today's drilling is now focusing on liquids plays, which make effective fracture conductivity far more important. The ways in which more conductivity can be delivered need to be revisited, be it with additives, proppant selection, or design approach. This paper reviews fracturing state-of-the-art methods for ultralow-permeability liquids-producing reservoirs and shows how fracture conductivity and economic optimization can be better achieved.