Design and Evaluation of Gravel and Frac Packs With a Fully Three-Dimensional Wellbore Simulator
- H. Hank Klein | Gary D. Cooper | Steven G. Nelson
- Document ID
- Society of Petroleum Engineers
- SPE Journal
- Publication Date
- September 1997
- Document Type
- Journal Paper
- 280 - 290
- 1997. Society of Petroleum Engineers
- 5.2 Reservoir Fluid Dynamics, 2.5.2 Fracturing Materials (Fluids, Proppant), 5.3.3 Particle Transportation, 1.6 Drilling Operations, 2.7.1 Completion Fluids, 2.4.5 Gravel pack design & evaluation, 4.1.3 Dehydration, 2.5.1 Fracture design and containment, 5.3.2 Multiphase Flow, 2.4.6 Frac and Pack, 1.8 Formation Damage, 3.2.5 Produced Sand / Solids Management and Control, 1.14.3 Cement Formulation (Chemistry, Properties), 2.2.2 Perforating, 4.1.2 Separation and Treating, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation, 2.4.3 Sand/Solids Control, , 4.1.5 Processing Equipment, 4.3.4 Scale
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During the gravel packing and fracturing processes in deviated wells the flows can follow complicated three-dimensional paths in the treating string. In this paper we present the formulation of a thee-dimensional numerical model of fluid and solids transport for evaluation and design of these completion events. The simulator tracks the slurry flow from the surface, throughout the wellbore, and into the perforations. It treats fluid return and loss into the formation. The model simulates fluid displacement, gravel settling, dune formation, bridging, fluid flow through packed solids and flow into and out of screens.
We present validation results against laboratory and field data for various fluids, deviations, pumping rates, and solids loading.
Gravel and frac packing have become an accepted method of sand control in wells in unconsolidated formations, Basically, gravel packing involves placing a screen at the bottom of the well and packing gravel around the screen and in perforations shot through the easing. In the case of frac packing, proppant is placed in a fracture outside of the casing and around the screen. The gravel prevents formation sand from entering the wellbore with the production fluid, and the screen presents a barrier to hold the gravel in place. The effectiveness of the packing procedure relies on the ability to place the gravel uniformly around the screen and in the perforations.
Highly deviated wells are commonplace in offshore wells. Also wells are being drilled horizontally to increase their production. However gravel packing in these wells has been less than successful. For low viscosity fluids, solids will settle on the low side of the well, and if there is a high leakofi, there will be insufficient velocity to tnsport the solids further down the well resulting in a bridge and premature screenout High viscosity fluids traJisport solids better than low viscosity ones, but gravel accumulates at the screen and perforations which can eventually form a bridge that prevents flirther slurry flow below the bridge. These effects result in incomplete placement of gravel, the presence of voids around the screen and unpacked perforations. Early screenouts attributable to bridging have also been observed in the frac packing process.
The success of the gravel and frac packing processes depends on the pumping rate of the slurry, the amount of solids loading in the slurry, the return rate, the size of the screen and washpipe, the viscosity of the fluids, the size and density of the gravel, and the leakoff of the carrier fluid into the formation. Thus it is desirable to find the optimum combination of parameters that will successfully complete highly deviated (as well as vertical) wells and prevent sand production for an extended period of time.
To date the procedures for gravel packing have been established through physical model tests and numerical simulation. The model tests have proved to be enlightening, but they are limited by scale size and the cost to conduct the tests. The operational numerical models can simulate the gravel pack procedure only in a two-dimensional manner. This can result in prediction and design limitations, since the transport in a deviated well is inherently three-dimensional, e.g., the fluid can flow down the wellbore, through the screen, around the washpipe, back into the large annulus and into the perforations.
In this paper we present the mathematical details of a fully three-dimensional numerical model of fluid and solids transport in a deviated wellbore that will identity the optimum combination of parameters for a successful completion. The model predicts gravel placement during the gravel and frac packing processes and slurry displacement during the fracturing process. The simulator tracks the slurry flow from the surface, throughout the wellbore, and into the perforations. It treats fluid return and fluid loss into the formation. The model simulates solids settling, dune formation, bridging, fluid flow through packed solids and flow into and out of screens.
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