Summary

The search for a cost-effective alternative to screens has been intensive in the sand-control field. Different systems have been proposed in the past, including various solutions based on permeable cement, but none of them have made a real breakthrough.

This paper presents a new permeable-cement system that has significant advantages over previous systems. In particular, this permeable cement was formed in a one-stage process, eliminating the need for a subsequent treatment to generate permeability. This permeable-cement system also has adequate strength and sufficient permeability for several sand-control applications. However, the durability of the permeable cement was evaluated and found to be poor. Some suggestions are made for possible applications of the permeable cement for both primary and remedial sand-control applications.

Background

The search for an alternative to screens has been ongoing for many years. One of the first inventions in this area was by Harnsberger and Payton (1969). These inventors slurried cement and sand in oil, and the mixture was subsequently suspended in an aqueous carrier fluid. The suspension then was to be forced into the formation and flushed with a surfactant solution to water-wet the cement to consolidate the injected sand and the weak formation. There were several subsequent patent applications along these lines, but no publications on the subject have been identified in the open literature, indicating that this idea has probably not been used commercially. One of the main drawbacks of this solution is that an overflush is required to water-wet the cement. Not only does this process increase the time required, but it is also difficult to ensure that all the cement/sand mixture has been activated.

A patent published many years later by Harris et al. (1994) described the use of very-high-quality foam (67% foam quality) cement to generate permeable cement. This process provides permeable cement in a one-stage process, but it is extremely difficult to mix and pump correctly because of the very high nitrogen volume in the slurry. In addition, the set cement has low compressive strength (<1.4 MPa) and the foamed slurry had a very low density. Subsequent inventions combined lower foam quality with acid-soluble material (Carpenter and Wilton 1996) and added oil-soluble particles and degradable polymer beads (Chatterji et al. 2001). Both of these solutions decrease the required foam quality, but both also require a post-treatment of acid or solvent. An acid post-treatment degrades the cement matrix. To date, no practical method to prepare permeable cement has been identified. This paper describes a permeable-cement system that overcomes many of the previous issues.

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