2013 Geothermal Technologies Office Peer Review Summary: Geothermal Cement

Transcription

1 2013 Geothermal Technologies Office Peer Review Summary: Geothermal Cement 1. Development of an Improved Cement for Geothermal Wells Awardee: Trabits Group, LLC Principal Investigator: George Trabits Contact Information Trabits Group PO Box Wasilla, Alaska (907) Project Team George Trabits, Trabits Group Geoff Trabits, Trabits Group Rene Trabits, Trabits Group Dr. Shirish Patil, University of Alaska Fairbanks Dr. Santanu Khataniar, University of Alaska Fairbanks Dr. Abhijit Dandekar, University of Alaska Fairbanks Dr. Matt Bray, University of Alaska Fairbanks Subawardee Petroleum Development Laboratory University of Alaska Fairbanks 425 Duckering Building PO Box Fairbanks, Alaska Project Objectives and Purpose Develop a novel, zeolite-containing lightweight, high temperature, high pressure geothermal cement, which will provide operators with an easy to use, flexible cementing system that saves time and simplifies logistics. The cement to be developed would have the following characteristics: 1) Thermal stability with little strength retrogression to 300 C. 2) Tensile strength to withstand temperature and pressure changes. 3) Low-density, low-viscosity slurries with low equivalent circulating densities (ECD) without the need for air or nitrogen foaming. 4) A single cement blend allowing density adjustments without adversely affecting slurry properties to eliminate the need for separate blends for lead and tail slurries. 5) Resistance to carbonation. 6) Accurate downhole densities throughout cement placement without significant changes in viscosity. 7) Water absorption capacity without retaining free water. 8) Good bonding to casing and formation. 9) Adequate compressive strength.

2 The development of an improved cement for geothermal wells is necessary to achieve the vision and goals of the Geothermal Technologies Program (GTP) under the Multi-Year Research, Development, and Demonstration (MYRDD) plan. An improved geothermal cement is in keeping with Goal 2 of the MYRDD Technical Plan to develop low-cost, highefficiency well construction which includes completion technology. Additionally, the development of an improved geothermal cement addresses Barrier C of the Site Selection Barriers. The MYRDD plan recognizes the current unsuitability of existing casing designs and materials for EGS and in particular the high cost of casing and cementing. A critical element of EGS is the creation of a reservoir by well stimulation which would most likely include hydraulic fracturing. The improved geothermal cement proposed has characteristics to withstand through-casing stimulation. 3. Technical Barriers and Targets Cementing high temperature geothermal wells today is largely limited to methods based on a technology developed in the early 1990 s by Brookhaven National Laboratory. This technology known as fly ash-modified calcium aluminate phosphate cement or CaP cement is described in US Patent 5,246,496 which was issued on September 21, Although CaP cements appear to perform effectively once placed they do have certain constraints which tend to increase cost and limit wide spread use. CaP cements exhibit sensitivity or in some cases incompatibility with common chemicals used as retarders or accelerators. In operating practices CaP cement cannot be contaminated with residual neat cement that may be leftover in pumping equipment from conventional completions. Operators, in effect, must sterilize equipment therefore increasing cost. CaP cement is ph sensitive as well as temperature sensitive. Operators have found that measured down-hole temperatures are critical in CaP cement batch formulation and that a variation in actual placement temperature verses batch formulation temperature can result in unpredictable setting time. Development of a zeolite-containing lightweight, high temperature, high pressure geothermal cement will provide operators with an easy to use, flexible cementing system that saves time and simplifies logistics. The requirement to sterilize pumping equipment before use, as with the CaP cement, will be eliminated. The following properties are the primary criteria for initial cement formulation screening: Zero percent free water Rheological properties of less than 200 reading at 300 rpm 24 Hour compressive strength greater than 500 psi Thickening time and consistency, end thickening under 70 Bc Slurry density less than 13.5 lbs/gal During the second stage of development the following tests are being performed: Rheological properties of cement slurry (shear stress versus shear rate) Slurry density measurement Slurry consistency and thickening time Compressive strength at 12 hour and 24 hour Tensile strength of set cement Percent free water measurement Response to retarders at high pressure and high temperature Quality of cement to casing bond Resistance to geothermal brines (long term stability) 2

3 Compressive strength retrogression over a three to six month period Determination of the optimum blend ratio of silica flour and other additives to zeolite for thermal stability Permeability of set cement Poisson s ratio and Young s modulus of set cement Thermal conductivity of set cement Initial cement formulation screening has been completed. Second stage development and testing is now in process. Long term testing of cement formulation for resistance to the effects of carbonation has been started. 4. Technical Approach The research and development is being conducted in five overlapping Tasks. These are: TASK 1 RESEARCH Literature Search Geothermal Cementing Practices and Constraints Mechanisms of Geothermal Well Failure TASK 2 DESIGN Compile Research Findings Modification of Project Tasks 3 and 4 TASK 3 DEVELOP Zeolite Sample Acquisition Zeolite Type Confirmation Zeolite Particle Size Preparation Initial Screening of Cement Formulations TASK 4 TEST Second Stage Cement Development Final Stage Cement Development TASK 5 DEMONSTRATE Laboratory Scale Demonstration Logistics and Ease of Use Field Demonstration Chena Hot Springs Resort High Temperature EGS Well Demonstration Ormat Technologies Key issues currently being addressed are: Compatible retarders at temperatures above 400 F. Additives for fluid loss control. Extension of base mixes and various silica sources to 572 F (300 C). 3

4 5. Technical Accomplishments Task 1 Research A comprehensive Literature Search was completed during A summary of geothermal cementing practices and constraints was completed during The mechanisms of geothermal well failure were researched during Task 2 Design Task 2 is an ongoing task where Tasks 3 and 4 are modified to take advantage of any improvements in additives, methods and testing procedures. Additionally, it is anticipated that refinement of the Development and Testing Tasks will continue as research results are factored into cement formulations. Task 3 Develop Task 4 Test Acquisition of the zeolite samples used in the cement development was completed in Zeolite type confirmation was completed by x-ray diffraction, x-ray florescence and scanning electron microscopic studies during 2010 and Three hundred pound splits of the bulk zeolite samples were shipped to CCE Technologies for preparation into the three sizes used in initial formulation screening. The zeolite sizes being used in initial blend tests were 5 microns, 10 microns and 44 microns. Two types of well cements being used in zeolite-containing cement formulations were acquired during These types are Class H and Class G. The Class H cement was supplied by Texas Lehigh Cement and the Class G cement by Lehigh Cement. A second Class G was obtained from Dykerhoff in Germany. The Dykerhoff cement will be compared to the U.S. Class G. Particle size distribution was completed for all cements. Five primary zeolites were tested each at three particle sizes: 5 µm, 10 µm and 44 µm. For each particle size tests were conducted at 15%, 27.5% and 40% cement replacement by zeolite. Primary screening tests were conducted at 13.5 ppg density and completed in October Work under Element One of Task 4 is in process. For this Element two of the screening stage zeolites were advanced to high pressure/high temperature (HPHT) cement formulation development and testing. All mixes to date provide adequate compressive strength to 400 F. UCA testing is being conducted that predicts compressive strength and strength development trends. Destructive compressive strength testing is being conducted to supplement UCA testing. Elastic properties between the two advanced zeolites are similar. HPHT consistency tests are being conducted as higher temperatures shorten cement working time. The effect of retarders is being tested. Two silica sources are being tested for thermal stability. Task Demonstrate Long term carbonation studies have begun using actual geothermal brine from Ormat s Brawley California field. Samples are being tested in brine that contains 1.5% CO 2 at 350 F. 4

5 6. Challenges to Date Industry partner ThermaSource was unable to participate and left the project in March The cement testing equipment in the ThermaSource lab was then unavailable to the project and it was necessary for the project to purchase testing equipment. The project also lost the cost share to be provided by ThermaSource. The project has successfully replaced the lost cost share and has met its cost share requirement. Additionally, the project was able to purchase all the necessary testing equipment but lead times required for fabrication of the testing equipment resulted in a schedule delay. The project has received an extension of the Period of Performance to September 30, Conclusion and Plans for the future The project has successfully completed a systematic series of cement formulation tests on five primary zeolites. Each zeolite was tested for three particle sizes: 5 µm, 10 µm and 44 µm. For each particle size, tests have been conducted at 15%, 27.5% and 40% cement replacement by zeolite. Screening tests were conducted at 13.5 ppg density for the primary screening criteria: 24 hour compressive strength Thickening time Free water Consistency Two zeolites were advanced to HPHT testing along with pozzolanic additives for enhanced strength. Work has begun on the effect of retarders to extend workability time at high temperature. Under Task 5 work has begun on the effect of long term carbonation of cement samples using actual geothermal brine at high temperature and high pressure conditions. Plans for the future: Data will be extended to 572 F (300 C) for base mixes with the addition of various silica sources. Further work will be conducted on compatible retarders at temperatures above 400 F. Fluid loss control additives will be explored. High demand pozzolanic additions will be investigated to accommodate cement slurries at densities below 13.5 ppg. X-ray diffraction and SEM analysis will be conducted on the hydrated cement samples for quantitative analysis of the phase assemblages. 8. Publications and Presentations Presentation - December 8, 2010 Anchorage, Alaska - Society of Petroleum Engineers, Alaska Section. Presentation March 9, 2011 Anchorage, Alaska Alaska Department of Natural Resources. Presentation December 7, 2011 Fairbanks, Alaska Alaska Support Industry Alliance. Presentation January 22, 2013 Bakersfield, California Baker Hughes Technical Services. 5