1. Technical Field
The invention relates to an apparatus and process for trapping fine particles entrained in hydrocarbon fluids produced from an unconsolidated hydrocarbon-bearing formation and more particularly to an apparatus and process for gravel packing a wellbore in fluid communication with an unconsolidated hydrocarbon-bearing formation.
2. Background Information
A hydrocarbon production well in fluid communication with an unconsolidated formation is typically completed by casing the wellbore, cementing the casing, and perforating the well at spaced intervals down the length of the production zone. Without further steps, formation fluids produced into the wellbore can entrain fine particles such as sand. The presence of fine particles in the produced fluids presents operational problems for the wellbore tubing and other production equipment. Furthermore, if sand is allowed to wash out from behind the casing, the washed out sections of the wellbore can cave and subsequently collapse the casing.
Gravel packing is a method of trapping entrained sand and other fine particles before the formation fluids enter the production string. Many gravel packing methods exist in the art as exhibited by the following list of U.S. Pat. Nos.:
______________________________________ 3,216,497 Howard et al 3,884,301 Turner et al 4,018,282 Graham et al 4,018,283 Watkins 4,046,198 Gruesbeck et al 4,350,203 Widmyer 4,428,431 Landry et al 4,438,815 Elson et al 4,522,264 McNeer ______________________________________
U.S. Pat. No. 4,018,283 to Watkins exemplifies a circulating gravel packing process. In general, a circulating gravel packing process places a tubing string terminating in a perforated base pipe into a wellbore. The base pipe extends concentrically through the wellbore down the length of the production zone. The base pipe defines an annulus in the wellbore between it and the production zone.
The gravel pack is performed by injecting a slurry containing gravel and a carrier fluid into this annulus. The gravel accumulates in the annulus while the carrier fluid leaks off through a screen into the base pipe and circulates back to the wellhead. Gravel packing is continued until the entire annulus adjacent the production zone is filled with gravel.
An optimum gravel pack is uniformly packed throughout the annulus. If the gravel pack contains non-uniformities, produced fluids carrying fine particles can channel through the gravel pack and into the production tubing. This defeats the filtering function of the gravel pack.
Circulating gravel packing processes continually confront the problem of bridging, duning and the formation of other non-uniformities, especially in wellbores deviating from the vertical. The upper end of a conventional base pipe often diverts the carrier fluid from the annulus before the slurry reaches the lower end of the annulus. Gravel prematurely builds up at the point of leakoff which creates a bridge in the upper annulus and a void in the lower annulus.
A circulating gravel packing apparatus and process are needed which enable proper leak off of the carrier fluid and which enable uniform gravel packing across the entire length of the annulus between the wellbore wall and the base pipe adjacent the production zone. An effective gravel packing apparatus and process are needed for highly deviated wells where the problem of bridging and duning is particularly acute.