Fracture Spacing and Well Spacing Optimization for Multifractured Horizontal Wells

Ashish Kumar, Deepen Gala, Dr. Mukul Sharma Research Showcase in Petroleum and Geosystems Engineering • September 8, 2015

Introduction

Pad drilled, multi-fractured horizontal wells are now commonly used for hydrocarbon production from low & ultra-low permeability reservoirs. The productivity of these wells is highly dependent on well spacing and fracture spacing, two factors over which operators have some degree of control. Too small a well spacing (better drainage) would result in high capital costs while too large a well spacing results in poor drainage of the reservoir. Objective of this work is to find out the optimum well spacing and fracture spacing in a real unconventional reservoir.

Hydraulic Fracture Modeling

Results

UTEFRAC-3D, a compositional hydraulic fracture simulator of the University of Texas at Austin is used to build a model for one of the stages of the well. Available geo-mechanical and reservoir properties, pumping schedule, fluid and proppant properties, wellbore and perforation details are incorporated into the model. Hydraulic fracture properties such as propped half length, conductivity and fracture height is obtained by calibrating the simulation model with surface pressures and injection rates.

Conclusions

Sensitivity to Reservoir Permeability

Acknowledgements

Hydraulic Fracturing & Sand Control Consortium at UT Austin.

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A single fracture was simulated with a specified fracture & well spacing. Boundaries are assumed to be no-flow boundaries (see dotted area below).

Reservoir Simulation

Flow Regimes: Multi-Fractured Horizontal Well

References

•  SPE-28389: Pressure Transient Analysis of Multifractured Horizontal Wells by Leif Larsen, T.M. Hegre

•  Production Analysis of Multi-Stage Hydraulically Fractured Horizontal Wells in Tight Gas Reservoirs by Fei Wang, Shicheng Zhang

•  SPE-174973-MS: A Comprehensive Study of Proppant Transport in a Hydraulic Fracture by C. A. J. Blyton, Deepen P. Gala, Mukul M. Sharma

•  Ribeiro, L.H. and Sharma, M.M. 2013. A new 3D Compositional Model for Hydraulic Fracturing with Energized Fluids. SPE Production and Operations 28, 259-267

The impact of different parameters such as reservoir permeability, net sand thickness on optimum well and fracture spacing is also analyzed. NPV is plotted as function of well spacing and fracture spacing to visualize the sensitivity of those on NPV and optimum is selected from the maximum NPV. The following conclusions can be drawn: •  The optimum well spacing and fracture spacing decrease with decrease in

reservoir permeability. •  The optimum penetration ratio decreases with increase in reservoir

permeability. •  The optimum well spacing and fracture spacing decrease with increase in

net sand thickness.

To analyze the effect of short fractures following two cases were simulated

•  Production is dominated by the long fractures only. •  Increment in oil production in Case-2 is around 2%, so only dominant

fractures for each stage need to be considered.

Methodology Optimization of well spacing and fracture spacing is done by maximizing the net present value (NPV) for a pad. Fracture Modelling is done to obtain the fracture dimensions and fracture conductivity. Production history matching of the oil, gas and water rates is performed for an existing fracture treatment to estimate the fracture dimensions and number of fractures per stage. The real costs for drilling and completing the well are used to estimate the upfront capital costs. The completion costs for different fracture length and different number of fractures per well is extrapolated based on these actual completion costs per unit fracture length. Reservoir simulations are then performed for different well and fracture spacing. The NPV is computed on the basis of the anticipated cash flow, discount rate and completion costs. The maximum NPV is then used to select the optimum well spacing and fracture spacing.

Well Spacing and Fracture Spacing optimization was done for three different reservoir permeability.

In case of multifractured horizontal well, flow rates decline very fast when fractures or wells start interfering each other. The time when production interference starts, will depend on Fracture Spacing and Well Spacing. Following flow regimes can be visualized in a multifractured horizontal wells.