DFIT, LOT, XLOT, Minifrac, Microfrac, Fracture Calibration Test: Navigating the Terminology
A bewildering variety of terms are used to describe tests in which a small volume of fluid is injected to create a hydraulic fracture: DFIT, leakoff test (LOT), extended leakoff test (XLOT), minifrac test, microfrac test, fracture calibration test, and more. These terms are commonly used interchangeably to refer to a fracture injection test. However, to be precise, they have slightly different meanings:
Diagnostic fracture injection test (DFIT): performed with clear water in a completed well. The term implies that the formation has low permeability and that the shut-in period will be long. The term was originally coined by Halliburton, but today it is widely used by companies across the industry.
Leakoff test (LOT): performed during the drilling of the well after setting a casing shoe and typically performed with drilling mud.
Extended leakoff test (XLOT): similar to a leakoff test, but with multiple cycles of shut-in and injection.
Fracture calibration test: performed with the fluid that will be used in a hydraulic fracturing treatment and is focused on inferring parameters that will be needed for designing the fracturing treatment.
Minifrac test: originally used to refer to a fracture calibration test. However, the term is commonly used to refer to any type of fracturing test (this is also true of the terms leakoff test and extended leakoff test).
Microfrac test: performed with a particularly small volume of fluid. Wireline tools can be used to perform microfrac tests, and different service companies have their own names for the tools used for these tests.
The variety of terminology, often used inconsistently, can sometimes lead to miscommunication even among experienced practitioners!
The gallery below shows excerpts and overviews from several important papers on injection tests, dating back to 1957 with a paper from M. King Hubbert, of Hubbert Curve fame. Going through the references, you can see terminology changing over the years. Early papers don’t even have a particular term for fracturing tests. For example: “stress measurements using the hydraulic fracture technique” (Zoback et al., 1977). In the list of references below, you can see the terminology evolving over time.
Evolution of injection test terminology over time.
Addis, M. A., T. H. Hanssen, N. Yassir, D. R. Willoughby, J. Enever. 1998. A comparison of leak-off and extended leak-off test data for stress estimation. Paper SPE 47235 presented at the SPE/ISRM Rock Mechanics in Petroleum Engineering, Trondheim, Norway, doi: 10.2118/47235-MS.
Alberty, M. W., M. R. McLean. 2014. The use of modeling to enhance the analysis of formation-pressure integrity tests. SPE Drilling and Completion 29 (4): 431-437, doi: 10.2118/167945-PA.
Almeida, Mauricio de Aguilar. 1986. Computer-aided analysis of formation pressure integrity tests used in oil well drilling. PhD Thesis, Louisiana State University.
Chenevert, Martin E., Leo J. McClure. 1978. How to run casing and open-hole pressure tests. Oil and Gas Journal 76 (10): 66-76.
Craig, David P., Ted D. Brown. 1999. Estimating pore pressure and permeability in massively stacked lenticular reservoirs using diagnostic fracture-injection tests. Paper SPE 56600 presented at the SPE Annual Technical Conference and Exhibition, Houston, TX, doi: 10.2118/56600-MS.
Godbey, J. K., H. D. Hodges. 1958. Pressure measurements during formation fracturing operations. Petroleum Transactions, AIME 213: 65-69.
Haimson, Bezalel, Charles Fairhurst. 1967. Initiation and extension of hydraulic fractures in rocks. Society of Petroleum Engineers Journal 7 (3), doi: 10.2118/1710-PA.
Harting, T. A., D. L. Cox, R. Murillo, T. L. Young, K. A. Adegbola, D. Schupp. 2004. Applications of mini-falloff test to determine reservoir parameters and optimize fracture designs in a tight gas field. Paper SPE 90455 presented at the SPE Annual Technical Conference and Exhibition, Houston, TX, doi: 10.2118/90455-MS.
Hickman, Stephen H., Mark D. Zoback. 1983. The interpretation of hydraulic fracturing pressure-time data for in-situ stress determination. In Hydraulic Fracturing Measurements, ed. M. D. Zoback and B. C. Haimson, 44-54. Washington D.C., National Academy Press.
Hubbert, M. K., D. G. Willis. 1957. Mechanics of hydraulic fracturing. Journal of Petroleum Technology 9 (6): 153-168.
Kehle, Ralph O. 1964. The determination of tectonic stresses through analysis of hydraulic well fracturing. Journal of Geophysical Research 69 (2): 259-273, doi: 10.1029/JZ069i002p00259.
Kunze, Kenneth R., Ronald P. Steiger. 1991. Extended leakoff tests to measure in situ stress during drilling. Paper presented at the 32nd U.S. Symposium on Rock Mechanics, Norman, OK.
Mayerhofer, M. J., M. J. Economides. 1993. Permeability estimation from fracture calibration treatments. Paper SPE 26039 presented at the SPE Western Regional Meeting, Anchorage, AK, doi: 10.2118/26039-MS.
McLennan, J. D., J.-C. Roegiers. 1982. How instantaneous are instantaneous shut-in pressures? Paper SPE 11064 presented at the 57th Annual Fall Technical Conference and Exhibition of the Society of Petroleum Engineers of AIME, New Orleans, LA, doi: 10.2118/11064-MS.
Moore, Preston L. 1973. Casing-seat testing- why and how. Oil and Gas Journal 21 (32): 72-74.
Morita, N., G-F. Fuh, P. A. Boyd. 1997. Safety of casing shoe test and casing shoe integrity after testingq. SPE Drilling and Completion 12 (4): 266-274, doi: 10.2118/22557-PA.
Nolte, Kenneth. 1979. Determination of fracture parameters from fracturing pressure decline. Paper SPE 8341 presented at the SPE Annual Technical Conference and Exhibition, Las Vegas, Nevada, doi: 10.2118/8341-MS.
Postler, D. P. 1997. Pressure integrity test interpretation. Paper SPE 37589 presented at the SPE/IADC Drilling Conference, Amsterdam, The Netherlands, doi: 10.2118/37589-MS.
Van Oort, Eric, Richard F. Vargo. 2008. Improving formation-strength tests and their interpretation. SPE Drilling and Completion 23 (3): 284-294, doi: 10.2118/105193-PA.
Zoback, Mark D., John H. Healy, John C. Roller. 1977. Preliminary stress measurements in central California using the hydraulic fracturing technique. In Stress in the Earth, ed. Max Wyss, 135-152. Birkhäuser Basel.