Use of Hydraulic Fracture Diagnostics to Optimize Fracturing Jobs in the Arcabuz-Culebra Field

Abstract

Abstract This paper presents the results of a study conducted to improve hydraulic fracturing and field development in the Arcabuz-Culebra Gas Field in Mexico. Hydraulic fracture mapping was performed on four stimulation treatments using a combination of tiltmeters (surface and downhole) and microseismic imaging. Fracture mapping was complimented by 3-D fracture modeling and geomechanical modeling. Data analyses resulted in recommendations regarding well positioning and hydraulic fracture design. Introduction Pemex Exploration & Production (PEMEX) is actively developing the Arcabuz-Culebra Field1, a fault-bounded gas field located in the Burgos Basin in the northern-eastern state of Nuevo Leon, Mexico (i.e., an area proximal to McAllen, Texas) as shown in Figure 1. Gas wells in the Arcabuz-Culebra field are completed in the vertically stacked reservoirs of the Wilcox Sands - a reservoir that commonly requires hydraulic fracturing to stimulate gas production in commercial volumes. Although many gas wells have been successfully drilled and completed in the field, PEMEX recognized that the continued economic development of low-permeability, over-pressured reservoirs characteristic of those in the Arcabuz-Culebra Field requires the efficient application of hydraulic fracturing, and effective well spacing and positioning. Typically, long hydraulic fractures can significantly increase well productivity in tight reservoirs. The resulting drainage pattern is elliptical and, therefore, accurate knowledge of fracture direction is required to optimize well spacing and field development. Well spacing and location are controlled by the in situ stress-state (which controls fracture geometry and direction), reservoir permeability, and the distribution and orientation of faults. Local variations in pore pressure due to compartmentalization and/or offset well production can result in large variations in stress that can significantly impact reservoir production, fracture geometry, and fracture direction. The primary tool used to "predict" fracture direction is a geomechanical model and several advanced diagnostic technologies are available to "measure" hydraulic fracture direction and geometry. By using these technologies, the economic value of the Arcabuz-Culebra Field would be maximized through improved well positioning, better hydraulic fracture treatment designs and optimized production strategies. Project Scope The technical approach integrated geomechanical modeling with hydraulic fracture mapping, fracture modeling and reservoir engineering to characterize hydraulic-fracture geometry, improve field-development practices and optimize fracture-treatment designs, as summarized in Figure 2. PEMEX staff worked in close cooperation with a team led by GRI to applied advanced technology solutions to well-completion challenges. This team included Pinnacle Technologies (tiltmeter fracture mapping, fracture and reservoir engineering), GeoMechanics International (geomechanics studies) and Branagan & Associates, (microseismic fracture mapping). Collectively, these companies will be referred to as the Arcabuz-Culebra Team. Geomechanical Analyses The approach to developing a geomechanical model for the Arcabuz-Culebra Field was multifold. The methodology consisted first of studying the regional geology and state of stress to assess lithology, regional faulting, and stress orientation trends. Second, analyses of various types of data from wells previously drilled into the field served to determine the full, local stress tensor (i.e., stress orientation and magnitude).