Gas Recovery From Tight FormationsA Function of Technology and Economics

Abstract

Summary Three major findings emerge from the study of the technology and economics of recovering natural gas from tight gas formations.1. A minimum threshold price, near $3.00/Mcf (in mid-1977 dollars) and equivalent to approximately $4.50/Mcf (in mid-1981 dollars), is required to make the tight gas resource attractive for investment.2. Beyond the threshold price, improvements in technology have a greater impact in terms of gas recovery than further increases in gas prices.3. The combination of increased gas prices and improved recovery technology provides the most effective means for accelerating production from this vast domestic natural gas resource - calculated at more than 400 Tcf in place.The technology improvements that have the largest impact on ultimate recovery are (1) improved ability to identify the net pay and characterize the reservoir, (2) capacity to stimulate multiple reservoirs from a common wellbore, (3) increased effective fracture length, (4) ability for fractures to intersect sand lens beyond the wellbore, and (5) optimization of field development. Background Large quantities of natural gas exist in tight (low-permeability) formations where the gas flow is too low for economical recovery by means of conventional technology. The basins containing these formations stretch westward from the Cotton Valley trend in Louisiana, through Texas, to the Uinta basin of Utah, and north through the northern Great Plains, crossing the border into Canada (Fig. 1). Declining natural gas production, higher gas prices, and new recovery technologies have focused interest on these resources.In the late 1960's and early 1970's, three attempts were made to stimulate tight formations by nuclear stimulation. Disappointing results ended the nuclear tests.In 1972, massive hydraulic fracturing (MHF) using volumes of fluids and proppants an order of magnitude or more larger than conventional was proposed. As a consequence, a joint government/industry test of MHF was conducted in the Piceance basin in 1974. The results of this test demonstrated that improvements could be achieved in the rate of gas flow. Since that time, MHF technology has been used widely in low-permeability but otherwise geologically favorable settings such as the Wattenberg field (north of Denver), the San Juan basin of New Mexico, and the Cotton Valley trend in east Texas and northern Louisiana.Despite the work to date, challenges posed by difficult geological settings - especially of the deep, tight, lenticular gas pays - have yet to be overcome. Even in the more geologically favorable basins - in the higher permeability and blanket type deposits fundamental improvements in recovery technology need to be pursued. Purpose and Methods This paper examines how improved technology and economics together can accelerate the contribution of the tight gas formations to U.S. energy supply. Overall results are presented for 13 tight gas basins for two levels of technology and three levels of economic incentives (represented by gas prices, although other incentives could be substituted). This is followed by a sensitivity analysis of specific technology improvements. JPT P. 1545^