Openhole Multistage Hydraulic Fracturing Systems Expand the Potential of the Austin Chalk
- Gian Franco Callarotti (Enervest Ltd) | Steven Millican (Enervest Ltd)
- Document ID
- Society of Petroleum Engineers
- SPE Hydraulic Fracturing Technology Conference, 6-8 February, The Woodlands, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 1.6.6 Directional Drilling, 3 Production and Well Operations, 4.3.4 Scale, 5.6.5 Tracers, 1.10 Drilling Equipment, 2.5.4 Multistage Fracturing, 1.6 Drilling Operations, 1.4.3 Torque and drag analysis, 1.10.1 Drill string components and drilling tools (tubulars, jars, subs, stabilisers, reamers, etc), 1.2 Wellbore Design, 4.1.2 Separation and Treating, 2.5.2 Fracturing Materials (Fluids, Proppant), 5.2.1 Phase Behavior and PVT Measurements, 2 Well Completion, 5.5.8 History Matching, 5.5 Reservoir Simulation, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 4.6 Natural Gas, 1.6.7 Geosteering / Reservoir Navigation
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The Austin Chalk formation has seen several active development booms over the past 35 years due to new technologies. Recently, a program was undertaken to test multistage fracturing technology in the Giddings Austin Chalk field to determine if sufficient additional reserves could be unlocked to spark another development boom. This paper highlights the challenges encountered during the project from the initial reservoir simulation and well candidate selection through system design and installation and treatment design.
The Austin Chalk formation has seen considerable horizontal development across Texas as operators chased areas of concentrated natural fractures. Significant quantities of hydrocarbons are apparently trapped in the tight carbonate matrix between the widely spaced fractures along the proven productive edge of the field. Many of the wells in these areas have poorly drained the Austin Chalk due to limited natural fracturing. Multistage fracturing has the potential to reach the insufficiently drained matrix blocks by isolating portions of formation between the natural fractures.
A total of 16 openhole multistage hydraulic fracturing completion systems have been run in the Giddings Austin Chalk field across four different counties in an effort to increase EUR's from existing wells and to extend the economic boundaries of the formation.
Simulation work done at the outset of the project pointed towards economic incremental recoveries from multistage hydraulic fracturing. This work also helped validate initial candidate selection. It was found that openhole multistage systems can be run into the Austin Chalk, but it was learned that due to high formation friction factors, careful design work was necessary to ensure that the completion equipment could be run to the desired depth. Results to date have shown that multistage fracturing can increase recovery from existing wells in poorly fractured areas as well as allow for economic development of previously uneconomic fringe areas.
The development of the Austin Chalk formation has relied on fractures and technology. A combination of natural and hydraulically induced fractures has been necessary for most wells to reach their full potential while seismic and horizontal drilling technologies allowed wellbores to be placed where they had the best chances of producing. The recent development of multistage fracturing systems has created the opportunity to further enhance recoveries.
The Austin Chalk is a Cretaceous-aged formation that produces along a NE-SW trend that is approximately parallel to the Texas Gulf Coast. The Giddings field is located in the central portion of this trend and stretches ~90 miles in length and ~30 miles in width (Figure 1 shows the extents of the Giddings field). Within the overall Austin Chalk formation, production comes from the Lower Austin Chalk, which is a hard, dense, micro-crystalline limestone. The reservoir units are characterized by dual porosity systems consisting of micro porous matrix and natural fractures. The matrix porosity is typically 3-8 percent while the permeability is normally less than 0.01 md. Initial production is dominated by flow from the natural fractures with the matrix providing support thereafter. The Giddings Austin Chalk ranges in temperature and depth from 220F at 7,500' TVD to greater than 350F at 14,000' TVD. Along the up dip edge of the formation, low GOR oil is produced, gradually transitioning to dry gas along the deepest, hottest parts of the reservoir.
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