Laboratory Studies of Fines Movement in Gravel Packs
- A.R. Jennings Jr. (Enhanced Well Stimulation Inc.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling & Completion
- Publication Date
- December 1997
- Document Type
- Journal Paper
- 275 - 281
- 1997. Society of Petroleum Engineers
- 1.6 Drilling Operations, 3 Production and Well Operations, 2.5.2 Fracturing Materials (Fluids, Proppant), 2.4.3 Sand/Solids Control, 2.7.1 Completion Fluids, 5.3.2 Multiphase Flow, 1.8 Formation Damage, 2 Well Completion, 3.2.5 Produced Sand / Solids Management and Control, 1.2.3 Rock properties, 5.6.9 Production Forecasting, 2.2.2 Perforating, 3.4.5 Bacterial Contamination and Control, 2.4.6 Frac and Pack, 5.1.1 Exploration, Development, Structural Geology, 2.4.5 Gravel pack design & evaluation, 3.2.3 Hydraulic Fracturing Design, Implementation and Optimisation
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Most high-permeability, high-deliverability, unconsolidated and loosely consolidated sandstone formations require gravel packing as part of the completion procedure. The gravel packs are designed to allow the soft formations to produce sand-free at economic production rates. Techniques and procedures used for gravel size selection are typically based on criteria which have been used by the industry for over 20 years.
Simple laboratory flow tests using clean gravel columns and fines from a variety of formations, however, indicate existing gravel-size selection guidelines are too conservative. Although the gravels selected are very efficient in preventing formation fines from entering the pack, the buildup of silt and fines at the gravel/formation interface can cause quick degradation of the effective permeability through the pack.
Improvements in gravel pack life can be obtained by using gravel with higher initial permeability, either by increasing the average size of the gravels used (i.e. larger sand grains) or through the use of more spherical particles (synthetic gravel). The laboratory tests reported in this paper suggest that both alternatives can be considered in gravel pack operations. It is a further premise of this paper that sufficient improvements have been made in gravel pack procedures in recent years to allow effective placement of the higher permeability gravels proposed.
Many of the hydrocarbon-bearing formations throughout the world with the greatest potential for producing oil and gas are loosely consolidated and unconsolidated sandstones. Most of these formations are composed of sand grains and silt with varying degrees of particle sorting and clay composition. Such sandstone and siltstone deposits are of recent geological age and though some are now buried deep below the earth's surface, most of the "Gulf Coast-type" sands have not been subjected to sufficient tectonic forces, pressures, temperatures, and time to tightly consolidate the formation rock. However, because of the high permeability and porosity of these rock types, they have made excellent reservoirs for the accumulation of large quantities of migrating oil and gas.
Although the loosely consolidated and unconsolidated formations are "soft" and of low intergranular strength, they are subjected to situ stresses and forces dependent upon their depositional and geological histories. Prior to invasion by the drillbit, the formations exist in equilibrium. With the drilling of wells and associated activity related to well completions and production, changes begin to occur in these formations as their hydrocarbons are produced.
The immediate impact of changes in pore pressure and stress distribution with initial production are not readily detectable in harder, more consolidated formations. However, in loosely consolidated and unconsolidated formations, even minor changes in stress magnitude and distribution with pressure drawdown and hydrocarbon production, can cause the formation to fail and to produce sand and silt with the formation fluids. Contributing factors to formation failure and sand production include magnitude of pressure drawdown during production, viscosity of the hydrocarbon, single or multi-phase flow, formation rock strength, pay thickness open to flow, cased hole or open hole, and others.
Much laboratory work and associated field applications have been performed for the determination and prediction of conditions to allow sand-free hydrocarbon production from soft, loosely consolidated formations. These or similar relationships have been applied to many formations throughout the world to allow sand-free production at economic rates without gravel packing and without immediate, catastrophic formation failure.
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