Optimal Hydraulic Fracture Angle in Productivity Maximized Shale Well Design

Abstract

In general, hydraulic fractures propagate perpendicular to the horizontal well axis whenever the drilling direction is parallel to the principal minimum stress plane. However, operators frequently drill horizontal wells parallel to lease boundaries resulting in slanted hydraulic fracture planes at angles less than 90 degrees from the well axis. This study provides a model for the inclined fracture case. It applies and further extends the unified fracture design approach for rectangular drainage areas, relating the dimensionless proppant number to the maximum productivity index in pseudo-steady state conditions. When simulating flow in shale reservoirs, the stimulated shale volume was represented as a rectangular drainage area that varies with changing angle, but preserves total area. Similarly, fracture length and width varies with changing angle, but total propped fracture volume stays constant. Results show that for any given set of reservoir and proppant properties along with a given proppant mass, as long as the created fractures drain the same stimulated rock volume, there exists a well direction resulting in maximized well productivity that is not necessarily parallel to the minimum stress direction. In addition, results yield two main correlations. The first one relates the optimal fracture angle to proppant number, for a given ratio of well spacing to primary-fracture spacing. In this way, operators can choose the drilling azimuth that would maximize production. The second correlation determines the optimal ratio of well spacing to primary-fracture spacing as a function of proppant number for a given fracture angle. This can be applied when selecting the optimum number of fracture stages given a well spacing plan and fracture angle. Two case studies show the application of these findings. In the end, this work provides a simple framework for well design incorporating slanted hydraulic fractures.

Pore Pressure Disturbance Induced by Multistage Hydraulic Fracturing in Shale Gas: Modelling and Field Application

“…According to the design method of casing program [26], the safety margin of equivalent density for gas kick is 0.05-0.10 g/cm 3 . This indicates that it would be safe for the infilling well drilling with similar designs (including drilling fluid density and casing program) of the nearby wells in the areas where the pore pressure disturbance is smaller than 1.05 (i.e., P/P 0 < 1 05).…”

“…Their targets are within the same formation. Well 81-2HF was drilled to 5005 m (TVD = 3873 81 m) at the third spud using oil-based mud (OBM) with a density of 1.47 g/cm 3 (Figure 10). And it was completed on June 12, 2015.…”

“…The flames of these burnings reached 2~6 meters, and the average burning time was nearly 70 min. The drilling fluid was weighted seven times, and its density increased from 1.36 g/cm 3 to 1.85 g/cm 3 (Figure 11). The nonproductive time due to these kicks reached 288 hours, and the average ROP of the third spud decreased to 5.17 m/h.…”

“…The shale gas production reached 7500 × 10 8 m 3 in America in 2016, which made up more than 40% of the total natural gas production of America [1]. The horizontal well factory and multistage hydraulic fracturing are the two most important technologies for shale gas production commercially [2][3][4].…”

Stress redistribution in multi-stage hydraulic fracturing of horizontal wells in shales

“…Multi-stage fracturing in horizontal wells is an important and effective completion method for compact, low permeability reservoirs (Cai et al 2009;Yao et al 2013;Koløy et al 2014;Li et al 2014;Sorek et al 2014;Zhang and Li 2014). The essence of hydraulic fracturing is to inject high-pressure fluids into a reservoir to create induced fractures around the wellbore.…”