This paper describes a one-trip, multizone gravel-packing technique designed for use in short-zoned, shallow, low-pressure wells. The system, which allows several zones to be completed with a single gravel-pack assembly, has been adapted for use in both standard and thermal applications.
In today's petroleum industry, optimizing completion operations without adversely affecting productivity provides several direct economic benefits. Combining procedural steps reduces the time required to perform the completion. Operational advantages are gained by reducing the opportunities for equipment malfunctions, well-control problems, and associated delays. Reduced exposure of the productive interval to completion fluids can also improve productivity. Finally, earlier initial production enhances project economics by accelerating the revenue stream. The one-trip, multizone gravel-packing technique described here allows several zones to be completed with a single gravel-packing assembly. Selective production or injection is achieved, however, as though the zones were completed separately. The basic design has proved to be adaptable to the development of modified systems for special applications. These include high-temperature steam systems, which use expansion joints and thermal packers, and the configuration of three- and four-zone hookups. The system has been run more than 500 times by major operators in several southern San Joaquin Valley fields in California. The requirement for this one-trip, multizone completion technique was born from the desire to streamline the lengthy completion operations being used. Basically, a dual-zone gravel-packed completion was required for the shallow, heavy-oil reservoirs. Because thermal stimulation was required for primary production, zonal isolation was necessary to facilitate future developmental plans, such as selective steam soaking and zone abandonment. In addition, the completions were complicated by low reservoir pressure (less than 500 psi [less than 3.45 MPa]), high fluid loss, and hole stability problems. Early completion programs involved completing each zone of the two-zone well separately. This system required the lower zone to be perforated and then the perforations to be washed. After another trip to run the gravel-pack assembly, the gravel pack was performed. Once the lower-zone completion was installed, a temporary bridge plug was set above the lower zone to isolate it from the perforating and perforation-washing procedures taking place on the upper zone. Thus, a retrieval trip was later required before the upper-zone gravel-pack assembly was run. To isolate the lower zone from the upper zone during gravel-pack operations, a drillable baffle plate (Fig. 1) was used on the bottom of the upper-zone assembly. This baffle plate provided a seal for the internal bore of the hookup, while the upper zone's sump packer provided an annular seal. Isolation would be achieved after the setting depth was reached and the sump packer set. Once the upper zone was completed, an additional procedural step was required to mill out the baffle plate. While these procedures were effective, they were also costly, with the bulk of the expense coming from rig time and multiple service charges. Completions performed in this manner took an average of 4 to 5 days with few major problems. An improved program was sought to complete these wells to lower costs, to reduce procedural steps, and to accelerate production.