Analysis of production data from hydraulically fractured horizontal wells in Marcellus Shale

Abstract

Unconventional reservoirs play an enormous role in hydrocarbon production in the United States. Marcellus Shale, a Devonian black shale found in the Appalachian Basin, has shown notable promise in the past few years. Shale is a complicated, naturally fractured reservoir with ultra-low matrix permeability. The gas is stored in the limited pore space of these rocks and a sizeable fraction of the gas in place may be adsorbed on the organic material. Shale gas reservoirs differ from conventional reservoirs in that massive stimulation treatments are required to achieve economic production. Horizontal wells are the most effective in providing access to the formation to perform multi-stage hydraulic fracturing treatments. The limited field experience with multiple hydraulic fractures in horizontal wells completed in Marcellus Shale indicates that significant increase in initial production can be achieved as the number of hydraulic fractures is increased. However, the production performance, particularly over longer time periods, is not well established. The objective of this study was to investigate the long term production performance of multiply fractured horizontal wells completed in Marcellus Shale. Historical production data and stimulation treatment information have been collected and analyzed for a number of horizontal wells both in West Virginia and Pennsylvania. A commercial reservoir simulator which accounts both for dual porosity behavior and the adsorbed gas was utilized to history match the production performance. Based on the results of the history matching, the long term production performances of the multiply fractured horizontal wells were predicted. The results were then utilized to investigate the production decline behavior of Marcellus Shale horizontal wells. A number of conventional as well as shale specific production decline models were considered in these investigations. The results indicated the presence of different flow periods. The hydraulic fractures appear to dominate the early production performance which is characterized by linear flow. Gas desorption appears to impact on production decline behavior during the intermediate period. The late production is influenced by the reservoir boundaries and is controlled by natural fracture properties. A single decline model often cannot predict the entire production behavior and conventional decline analysis based on the early production data can lead to significant over-prediction of the future production rates or reserves. The results of this study can be utilized as guideline to investigate the feasibility horizontal wells with multiple hydraulic fractures and optimize the production from the shale formation.