Methods for shut-in pressure escalation analysis
Methods for using shut-in pressures to determine uncertainties in a hydraulic fracturing process in a shale reservoir are described. Data commonly collected during multistage fracturing is used to calculate propped fracture height and induced stresses, as well as other variables, in the presence of horizontal stress anisotropy. These variables can then be incorporated into reservoir simulations to improve the fracturing monitoring, forecast hydrocarbon recoveries, or modify fracturing plans.
1 . A method of producing oil, comprising:
a) fracturing a well in a reservoir in n fracturing stages and measuring instantaneous shut-in pressure (ISIP) data at an end of each of said n fracturing stages;
b) inputting said ISIP data into a software program stored in a non-transitory memory of a computer,
c) said software program matching said ISIP data by varying stress plateau and escalation using Eq. 1:
Δ
σ
shadow
(
n
)
=
Δ
σ
plateau
(
1
-
ε
1
-
n
Escalation
)
Eq
.
1
wherein;
n is a stage number, Δσ plateau is a total value of stress interference for n fracturing stages, Δσ shadow is a stress interference contribution for each of n fracturing stages, and Escalation is how quickly stress interference approaches a stress plateau;
d) estimating fracture height and estimating horizontal-stress anisotropy by comparing said ISIP data for each of said n fracturing stages against stress plateau type curves and escalation type curves;
e) inputting said estimated horizontal-stress anisotropy and said estimated hydraulic-fracture height into a reservoir model software and optimizing a reservoir fracturing plan;
f) fracturing a next stage of said well or fracturing a similar well in said reservoir with said optimized reservoir fracturing plan; and
g) producing oil from said well or said similar well.
2 . The method of claim 1 , wherein ISIP is a pressure value past an early rapid fall off as determined by extrapolating a slope at an end of a pressure pulse caused by shut-in.
3 . The method of claim 2 , wherein in step d) fracture height, fracture length, and fracture area are also estimated.
4 . The method of claim 2 , wherein ISIP is measured at the surface, downhole, or both.
5 . The method of claim 2 , wherein if a stress load is less than half a net-pressure in said well at shut-in, fracture reorientation is limited, and said method may proceed, but if not, said method is discontinued, wherein said stress load is net pressure in a fracture stage just prior to the start of a subsequent fracture stage.
6 . The method of claim 2 , wherein said optimized fracturing plan uses one or more modified parameter(s) selected from the group consisting of: cluster number per stage, cluster spacing, stage spacing, fracturing pressure, fracturing fluid type, fracturing fluid volume, fracturing fluid viscosity, proppant type, proppant mass, proppant concentration, pumping rate, pumping schedule or combinations thereof.
7 . The method of claim 1 , wherein ISIP is determined after each of n stages of a diagnostic fracture injection test (DFIT), wherein said ISIP is a pressure value past an early rapid falloff as determined by extrapolating a slope at an end of a pressure pulse caused by shut-in, and wherein said DFIT comprises injecting a volume of fluid at a low rate through perforations in a cemented casing to create a small-scale hydraulic fracture, thereby obtaining ISIP data for each of said n stages of said DFIT.
8 . The method of claim 7 , wherein in step d) fracture height, fracture length, and fracture area are also estimated.
9 . The method of claim 7 , wherein ISIP is measured at the surface, downhole, or both.
10 . The method of claim 7 , wherein if a stress load is less than half a net-pressure in said well at shut-in, fracture reorientation is limited, and said method may proceed, but if not, said method is discontinued, wherein said stress load is net pressure in a fracture stage just prior to the start of a subsequent fracture stage.
11 . The method of claim 7 , wherein said optimized fracturing plan uses one or more modified parameter(s) selected from the group consisting of: cluster number per stage, cluster spacing, stage spacing, fracturing pressure, fracturing fluid type, fracturing fluid volume, fracturing fluid viscosity, proppant type, proppant mass, proppant concentration, pumping rate, pumping schedule or combinations thereof.
12 . The method of claim 1 , wherein in step d) fracture height, fracture length, and fracture area are also estimated.
13 . The method of claim 1 , wherein said ISIP is measured at the surface, downhole, or both.
14 . The method of claim 1 , wherein if a stress load is less than half a net-pressure in said well at shut-in, fracture reorientation is limited, and said method may proceed, but if not, said method is discontinued, wherein said stress load is net pressure in a fracture stage just prior to the start of a subsequent fracture stage.
15 . The method of claim 1 , wherein said optimized fracturing plan uses one or more modified parameter(s) selected from the group consisting of: cluster number per stage, cluster spacing, stage spacing, fracturing pressure, fracturing fluid type, fracturing fluid volume, fracturing fluid viscosity, proppant type, proppant mass, proppant concentration, pumping rate, pumping schedule or combinations thereof.
16 . A method for producing oil, comprising:
a) fracturing a well in a reservoir in n stages and measuring instantaneous shut-in pressure (ISIP) data at an end of each of said n fracturing stages;
b) estimating fracture height and horizontal-stress anisotropy based on said ISIP data and comparison to type curves for stress interference and type curves for escalation;
c) optimizing a reservoir fracturing plan using said estimated horizontal-stress anisotropy and said estimated hydraulic-fracture height to obtain an optimized reservoir fracturing plan;
d) fracturing a next stage said well or fracturing a second well in said reservoir with said optimized reservoir fracturing plan; and
e) producing oil from said well or said second well.