The objective of this project is to demonstrate that a coiled tubing microhole drilling rig can be used to drill shallow (800 ft) instrumentation wells for the installation of a microhole vertical seismic profile array in order to monitor the movement of injected carbon dioxide into an oil reservoir for the purposes of enhanced oil recovery and carbon dioxide sequestration. As more CO2 enhanced oil recovery projects are started and CO2 sequestration proceeds, the need for less expensive monitoring wells will increase and the economics of using microhole wells will appear more favorable.
Los Alamos National Laboratory (LANL), Los Alamos, NM
The use of production and injection wells for seismic data acquisition has a number of disadvantages. Deploying seismic sensors and other logging-type tools interrupts field operations, resulting in loss of money through temporarily stopped production and idle time for expensive equipment and personnel. Production and injection wells often are not positioned in the most advantageous locations for obtaining reservoir data. Conventional wells dedicated to seismic monitoring are expensive to drill.
Microholes (wellbores less than 3½-inch diameter) have the advantage of being relatively inexpensive to drill, and locations and completion designs can be selected for optimal acquisition of seismic data. In previous DOE-funded projects, the project performer has demonstrated that coiled tubing microdrilling of wells as small as 1¾-inches in diameter and as deep as 800 ft can be achieved. The team also successfully field-tested geophysical micro-instrumentation in microholes cased with 1¼-inch tubing.
Los Alamos entered into an agreement with Whiting Petroleum Company to drill several microholes with a purpose-built coiled tubing drilling rig in order to establish a seismic monitoring program. The wells are located on the Wickett lease in North Ward Estes field in the Permian Basin of West Texas. A total of four wells were drilled to various depths between 300 ft and 1,000 ft. Each new microhole was equipped with geophones, and a passive seismic survey is being used to monitor the CO2 flood. Injection of CO2 for enhanced oil recovery is scheduled to begin in the second quarter of 2007. The results from the initial tests are expected by August 2007, and significant commercialization interest is already being indicated.
The overall objective of this project is to demonstrate the technical and economic feasibility of a highly mobile, self-contained, microhole drilling system as an enabling technology for commercially viable seismic-data acquisition. Succeeding in these objectives will result in reduced access (well) cost and improved quality of data. Air-filled microholes completed with PVC (or other nonmetallic casing) are expected to provide the lowest noise environment possible for retrievable seismic instrumentation.
The motivation to examine microholes for seismic data acquisition comes from providers of geophysical data to the oil and gas industries. They seek low-cost access to the subsurface for the emplacement of seismic instrumentation for a variety of purposes: conventional reflection surveys, natural and induced seismicity mapping, vertical seismic profiling, and crosswell imaging. These are all enhanced with the use of deep seismic sensors. Emplacement of seismic instrumentation in the subsurface results in a highly attenuated natural surface, cultural noise-reduced seismic-signal travel paths (through highly attenuating surface layers), and a greatly improved signal-to-noise ratio. Conventional wells are usually too costly, and existing wells seldom provide the instrumentation sites required at an acceptable cost. Microholes have the advantage of being fit for the purpose of subsurface deployment of instrumentation in the location required at a substantially lower cost.
A total of four new microholes were drilled to an average depth of 1,000 ft in North Ward Estes field located near Midland, TX, in the Permian Basin. One hole was drilled only to a depth of 300 ft, because of equipment failure of the purpose-built coiled tubing drilling rig. The shallow well will be used to help identify the source of passive seismic sources. The field work for this project has been completed and a Final Report with the results from the investigation has been submitted.