Oil and gas flow through fractures and along interfaces in well cement
- Univ. of New Mexico, Albuquerque, NM (United States)
- Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
A number of wells at the Strategic Petroleum Reserve (SPR) have shown sustained, positive pressure (referred to as sustained casing pressure or SCP) in the cemented annulus behind the production casing. To better understand how SCP may develop for SPR conditions, we conducted gas and oil flow tests on cement specimens with flaws including cement fractures and discrete interfaces along a cement-steel contact. Many specimens were tested initially with gas, followed by oil, and finally with gas again to identify how the fluid type may affect the flow through flaws in the well cement. Nitrogen was used as the gas, and silicone oil with properties similar to typical crude oil was used in most tests. One set of measurements were made with crude oil. Composite steel-cement specimen with corroded steel were also tested. For both gas and oil tests, the measured flow test data were used to interpret permeability and, assuming the cubic law for flow between parallel plates, the corresponding hydraulic aperture of the flaw. The hydraulic apertures for the flawed specimens ranged from about 20 to >100 μm, which corresponds to permeabilities of about 10-14 to 10-12 m2, respectively; these hydraulic apertures are consistent with the range of values interpreted from field measurements on leaky wells. Observed differences between the flow of gas and oil were attributed to a number of factors, including non-linear flow of gas, possible blocking of flow paths by solids within the crude oil, two-phase gas and oil flow and the presence of residual oil in the cement flaw. Furthermore, we determined that corroded steel itself is permeable. Using input values consistent with the gas and oil flow measurements, we conducted one-dimensional simulations of gas and oil flow through cemented annulus systems to investigate the role of flaw size and fluid type on the expected response (i.e., pressure build-up) in the annular cement.
- Research Organization:
- Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
- Sponsoring Organization:
- USDOE Office of Fossil Energy (FE), Petroleum Reserves
- DOE Contract Number:
- AC04-94AL85000
- OSTI ID:
- 1489868
- Report Number(s):
- SAND-2018-3264; 671157
- Country of Publication:
- United States
- Language:
- English
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