Optimizing Spacing of Multistage-Fractured Horizontal Wells in Gas Reservoirs

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 171688, “Optimizing Spacing of Horizontal, Multistage-Fractured Wells in Gas Reservoirs,” by Maryam Alghannam and Zillur Rahim, Saudi Aramco, prepared for the 2014 Abu Dhabi International Petroleum Exhibition and Conference, Abu Dhabi, 10–13 November. The paper has not been peer reviewed. The growing demand for gas in Saudi Arabia and the availability of multistage-fracturing (MSF) horizontal-well technology have spurred the development of tight gas reservoirs throughout the country. Draining the reservoir efficiently by use of MSF strongly depends on well spacing, especially for low-permeability reservoirs. This paper gives the recommended MSF horizontal-well spacing for several development scenarios in Saudi Arabian gas-reservoir environments. Theoretical Background There are four different flow regimes for multiple-fracture systems without wellbore storage: early linear, early radial, formation linear, and pseudoradial flow (Fig. 1). The initial flow period observed is the linear flow, where fluid flow toward the fractures in the formation is perpendicular to the fracture planes. This flow exists when each fracture behaves independently and most of the fluid entering the wellbore comes from the fractures (when the fracture-tip effects have not yet affected the pressure behavior). After the start of the flow into the fracture tips, the early radial flow develops while there is still no communication between fractures. This flow regime may occur briefly or it may not occur at all, depending on the fracture length and spacing. Subsequently, formation linear flow develops after the fracture interference has been felt and the flow becomes normal to the horizontal well. Finally, the pseudoradial-flow regime develops in the formation, where the flow appears radial toward the entire well/fracture system. During this flow period, the composite fracture system behaves as if it were a single fracture. The flow eventually will reach pseudosteady state when it hits the reservoir boundaries or interferes with surrounding wells. The rate at which the flow regime develops, from the start of production under transient conditions until it reaches reservoir depletion under pseudosteady state, is highly dependent on well spacing and well and reservoir characteristics.