Methods to Enhance Wellbore Cement Integrity with Microbially-Induced Calcite Precipitation (MICP)
Project Number
DE-FE0024296
Last Reviewed Dated
Goal
The goal of this project is to develop improved methods for sealing compromised wellbore cement in leaking natural gas and oil wells, thereby reducing the risk of unwanted upward gas migration. Integrated laboratory testing, simulation modeling, and field testing will be conducted to achieve this goal.
Performer(s)
Montana State University (MSU), Bozeman, MT 59717
Montana Emergent Technologies, Butte, MT 59701
Background
Microbially-Induced Calcite Precipitation (MICP) was shown to successfully seal a sandstone fracture in the first attempted downhole deployment of the technology in April 2014. Preliminary laboratory studies indicate that the elevated pH environment produced by cement enhances the MICP process. This project will test MICP for gas/fluid mitigation of compromised cement in an existing well that has regions of poor cement contact as measured via cement bond logs and shows ~300 psi natural gas pressure in the annulus. Pressure response, cement bond logs, sidewall cores, gas flow rate reduction, and parallel laboratory experiments will all be used to evaluate the MICP seal.
Impact
Gas migration, also called sustained casing pressure or sustained annular pressure, indicates there is hydraulic communication between the formation and the annulus because of inadequate zonal isolation. The escape of hydrocarbons to the surface or into groundwater aquifers resulting from poor cement placement, aging cement, or damage to the cement is a significant problem and the success rate of squeezing cement to fix leaks is less than 50 percent due to difficulties in getting cement to the proper locations. There is a need for new solutions for sealing leaking wells and, specifically, new methods to fix difficult-to-seal underground leakage pathways such as micro-fractures. MICP could be one solution to these problems. MICP offers a low viscosity solution that could possibly be injected further from the wellbore creating a larger and more permanent seal. The MICP technology could also open up other commercially-attractive applications. Successful demonstration of MICP-based sealing technology to enhance wellbore integrity will provide the following benefits:
MICP, because of its low viscosity, will enhance wellbore integrity by penetrating difficult-to-seal underground leakage pathways such as micro-fractures.
Unwanted upward migration of formation gases and fluids will be mitigated, thereby reducing environmental risk to overlying ground water supplies and release of greenhouse gases.
Accomplishments (most recent listed first)
On November 30, 2018, the Rexing #4 well was re-perforated and a pressure-flow test was conducted. The pressure was observed to be between 1400 psi and 1600 psi. Injection was turned off December 2018 and has not resumed. When injection resumes, production monitoring will take place.
The third field test of the MICP process was conducted in September 2018 at the Rexing #4 injection well, where the MSU team attempted to complete the repair of a suspected channel in the wellbore cement. In the December 2017 field work, 95 gallons of microbes and 195 gallons of urea and calcium solution were injected. To accomplish the new project objective of more complete sealing, larger volumes of solutions were injected in 2018. This required modification of the delivery system from a batch process delivered through a bailer system to a continuous injection process. There, the biomineralization solutions were staged and injected down a one-inch concentric tubing string placed inside the 2 7/8’’ tubing string, with both strings isolated by a packer.Rexing #4 well head in September 2018. A workover rig, the mobile laboratory, and a frac tank filled with 100 bbl of fresh water were on site during the field work.
The second field test of the MICP process occurred late November-early December 2017 at the Rexing #4 well near Owensville, Indiana. The Mobile Mineralization Operations Center was deployed for the first time during this field test. The results of the second field test were somewhat inconclusive. After a total of 25 inoculum injections and 49 calcium solution injections, the flow-to-pressure ratio of the system decreased from 10.4 x 10-3 gpm/psi to 3 x 10-3 gpm/psi, a reduction of approximately 70%. On day four, however, after several failed bailer deliveries, it was observed that there was a reduction in injection pressure. The cause of the pressure loss was unknown, though possible explanations include breaking down the newly-formed MICP mineral seal, a new fracture formed in the wellbore cement, or channeling in the sandstone.
The Mobile Mineralization Operations Center was reliever to Bozeman, MT the last week of October. The trailer built by, Becker Custom Trailer, is expected to increase the technology readiness level of the MICP technique from 5 to 7.
Mobile Mineralization Operations Center
MSU has designed and fabricated a new reactor system to measure and visualize the formation of MICP within a channel engineered in a cement core. The reactor and core system is compatible with X-Ray Computed Tomography (X-Ray CT) to monitor the distribution of mineral precipitate and subsequent reduction in porosity along the flowpath of the channel.
MSU has designed and fabricated a new reactor system to measure and visualize the formation of MICP within a channel engineered in a cement core. The reactor and core system is compatible with X-Ray Computed Tomography (X-Ray CT) to monitor the distribution of mineral precipitate and subsequent reduction in porosity along the flowpath of the channel.
During the week of April 11, 2016, the MSU research team mobilized equipment and performed the MICP treatment experiment at the Gorgas #1 well. Over the course of five days, biomineralization fluids and microbial growth media components were delivered to the interval of interest using a delivery bailer method. The experiment was successful, and three major findings were observed over the course of the five days:
Injectivity was significantly reduced (1.28 gpm to 0.75 gpm down to less than 0.05 gpm) after MICP treatment. The injection flow rate had to be decreased as pressure increased in order to remain below a maximum pressure (81.6 bar (or ~1200 psi)) that could have potentially initiated a fracture in the shale formation that was dominant in this interval.
A comparison of Ultrasonic Imager logs taken before and after MICP treatment indicated significant increase in the deposition of precipitated solids in the compromised cement region after sealing.
Pressure fall-off tests after MICP treatment met the Colorado definition of Mechanical Integrity for shut in wells which is “less than 10% pressure fall off in 15 minutes.”
MICP Field Test 1 Site at the Gorgas Power Plant near Jasper Alabama
MSU has developed a larger wellbore cement analog system (see below) to test the MICP process. The system consists of a 4 inch (10.16 cm) diameter outside casing and a 2.5 inch (6.35 cm) diameter inner PVC delivery pipe. This results in a 0.44 inch (1.18 cm) gap into which well cement can be placed. Initial positive results demonstrated significant permeability reduction and observed calcite precipitation in a wellbore annulus defect of 250 microns.
Initial laboratory test to determine the effectiveness of MICP seals have shown that over the course of a 223 hour experiment, the permeability of 100 μm annuli was reduced by five orders of magnitude after inoculation with S. pasteurii culture.
Construction of wellbore cement analog systems has been completed. These analogs are 1 inch (2.54 cm) core plugs designed with annular space between well casing steel and cement and cement and formation sandstone. Annuli will be varied in size to replicate fractures and various debonding spacing.
Preliminary experiments showed that the elevated pH environment produced by cement enhances the MICP process.
Two new reactor systems that simulate more realistic field type conditions were developed. The first reactor system has a controllable gap between cement and steel surfaces (as contrasted to the existing reactor’s cement polycarbonate interface). The second reactor system mimics cement between a surface casing and inner casing and will allow testing for 2020.
Current Status
MSU has completed the project including all laboratory studies, simulation modeling, and field data analysis. A manuscript related to dissemination of the results and a Final Technical and Scientific report highlighting project results was received. MSU continues to seek commercial applications for the MICP process.
