Life-Cycle Decline Curve Estimation for Tight/Shale Reservoirs

Abstract

Low-permeability (tight) and shale (gas and oil) reservoirs have emerged as a significant source of energy in North America. Recent advances in technology, such as long horizontal lateral/multi-lateral drilling combined with hydraulic fracturing, and new surveillance techniques, have enabled commercial production from ultra-low permeability reservoirs, previously considered source or cap-rock, not reservoirs. Forecasting well production for reserves estimation, hydraulic fracture stimulation optimization, and development planning remains a challenge because of complex reservoir behavior and flow geometries associated with current wellbore architectures/stimulation treatments used to exploit tight formations. Depending on the completion design, transient flow periods can last for weeks to years, and hence traditional methods requiring boundary-dominated flow are strictly inapplicable for most of the commercial life of many wells completed in tight formations. Recently, several analytical (type-curve, flow-regime analysis and simulation) and empirical approaches have been introduced to match and forecast tight reservoir production. The challenge is to develop routine techniques that can be used to forecast tight formation production, while adequately addressing the complex physics of the problem. In this work, we build on recent attempts to combine analytical and empirical methods ("hybrid" methods) for forecasting tight/shale gas reservoirs completed with multi-fractured horizontal wells. We forecast the homogenous completion (equal hydraulic fracture length) case using established analytical procedures for transient linear flow (pre fracture interference), combined with the Arps decline curve for late-time (boundary-dominated) flow. We also examine the heterogeneous completion (unequal hydraulic fracture length) case to establish the impact of heterogeneities on decline characteristics post fracture-interference. Finally, we present an innovative method for designing hydraulic fracture and well spacing.

Simplified Forecasting of Tight/Shale-Gas Production in Linear Flow

“…In the preceding decade, significant advances have been made in the development of analytical methods for analyzing production data and long-term forecasting from multifractured horizontal wells in unconventional reservoirs (Medeiros et al 2008;Ozkan et al 2011;Bello and Wattenbarger 2008). As mentioned by Ambrose et al (2011), despite these advances, the empirical methods are still the most popular methods for forecasting multifractured horizontal wells. For the purpose of tight/shale-gas reservoirs, where transient flow can last for a long time, the classic Arps decline-curve approach (Arps 1945) is not applicable, simply because its application is limited to boundary-dominated flow.…”

“…These techniques have been applied to horizontal wells with multiple fractures in tight formations, but tend to yield nonunique forecasts because of the number of parameters in the equations (Ambrose et al 2011). For example, there are four parameters to be determined for the power-law and three for the stretched-exponential method.…”

Shut-in based production optimization of shale-gas systems

“…Many operators tend to avoid numerical models in favor of these types of models due to their ease of construction and maintenance (Ambrose et al, 2011), as well as ease of use in history matching of production data, i.e. parameter estimation, and estimation of original gas in place.…”

Multiwell Analysis of Multifractured Horizontal Wells in Tight/Shale Gas Reservoirs

“…They used the concept proposed by Ambrose et al (2011) to divide a heterogeneous completion into different divisions with different durations of linear flow and then suggested that any of the hybrid methods can be applied to any of the divisions. For this purpose, a number  j is associated with each division which indicates the ratio of drainage area of that division to the total drainage area.…”

“…The fractures for both wells are identical and both wells have the same fracture spacing. Based on the concept of dividing the systems into different divisions as per Ambrose et al (2011) and Nobakht et al (2011b), the reservoir/completion geometry shown in Figure 1 is divided into three divisions as shown in Figure 2.…”