US 12,442,950 B1 · Evaluation method for relative contributions of heat sources based on helium and application thereof

Abstract

An evaluation method for relative contributions of heat sources based on helium and application thereof, belonging to the technical field of helium origin identification, migration mechanism, and accumulation process analysis. Relative heat contribution values of the mantle and the crust to a basin geothermal system are estimated by combining 3He/enthalpy ratios calculated according to the formula (1) and the heat balance equation, and an evaluation method for relative contributions of heat sources of helium in the context of deep thermal fluid activities is further improved. A detection device is suitable for deep geothermal resource exploration, thermal fluid activity monitoring in an early stage of oil and gas field development, and geological science research. By precisely evaluating relative contributions of a mantle source and a crust source, combined with temperature and pressure data, a scientific basis is provided for resource development, and exploration risks are reduced.

An evaluation method for relative contributions of heat sources based on helium, comprising a non-transitory computer readable medium operable on a computer with memory for the evaluation method for relative contributions of heat sources based on helium, and comprising program instructions for executing the following steps of:

Step 1:
performing a geological survey to confirm the presence of deep channel communication generated in a study region in the context of major faulting and the presence of development and evolution of mud diapirs and upward migration of thermal fluid;
Step 2:
collecting a sample from a reservoir of a typical well in the study region separating and purifying the sample;
Step 3:
testing and analyzing the sample to obtain the content of CO2, 3He, and 4He;
Step 4:
calculating 3He/enthalpy ratios of samples in different depths by a formula (1) and concentrations of CO2 and 3He of the samples, wherein the formula (1) is expressed in a dimensionless form, φ=f/(RT), which is divided into two parts, namely an ideal gas part φ° and a residual part φr, so φ:
f
⁡
(
ρ
,
T
)
R
⁢
T
=
ϕ
⁡
(
δ
,
τ
)
=
ϕ°
⁡
(
δ
,
τ
)
+
ϕ
r
(
δ
,
τ
)
(
1
)
wherein δ=ρ/ρc, and τ=Tc/T;
δ is a reduced density, and τ is a reversely reduced temperature;
and ρ is a density under reservoir conditions of a stratum, and T is a temperature under the reservoir conditions of the stratum;
and r is a residual value;
Step 5:
using the following reference constants required by the formula (1):
Tc=647.096K;
ρc=322 kg m−3;
R=0.46151805 kJkg−1K−1 (2)-(4)
wherein Tc is a critical temperature, and ρc is a critical density;
Step 6:
obtaining an equation of the ideal gas part φ° from a specific isobaric heat capacity equation
c
p
o
in an ideal gas state:
ϕ°
=
ln
⁢
δ
+
n
1
∘
+
n
2
∘
⁢
τ
+
n
3
∘
⁢
ln
⁢
τ
+
∑
i
=
4
8
⁢
n
i
∘
⁢
ln
[
1
-
e
-
γ
i
o
⁢
τ
]
(
5
)
wherein the
c
p
o
is fitted through a nonlinear least square method to determine coefficients b0 and bi and an index βi;
let
n
3
∘
=
b
0
-
1
,
where i is an integer from 1 to 8,
n
i
+
3
°
=
b
i
,
and
⁢
γ
i
+
3
∘
=
β
i
/
T
c
,
to simplify the formula;
and ni° is a simplified coefficient, γi° is a simplified index, and the formula (5) is obtained;
Step 7:
representing a form of the residual part φr as follows:
ϕ
r
=
∑
i
=
1
7
⁢
n
i
⁢
δ
d
i
⁢
τ
t
i
+
∑
i
=
8
51
⁢
n
i
⁢
δ
d
i
⁢
τ
t
i
⁢
e
-
δ
c
i
+
∑
i
=
52
54
⁢
n
i
⁢
δ
d
i
⁢
τ
t
i
⁢
e
-
α
i
(
δ
-
ϵ
i
)
2
-
β
i
(
τ
-
γ
i
)
2
+
∑
i
=
55
56
⁢
n
i
⁢
Δ
b
i
⁢
δ
⁢
ψ
(
6
)
wherein di, ti, αi, γi and ∈i are parameters;
ψ is a special heat function, Δ is an arbitrary difference function, and ci is an index, and;
Step 8:
calculating values of functions Δ, θ, and ψ of related nonanalytic terms:
Δ=θ2+Bi[(δ−1)2]ai
θ=(1−τ)+Ai[(δ−1)2]1/(2βi)
ψ=e−Ci(δ−1)2−Di(τ−1)2 (7)-(9)
wherein Ai, Bi, Ci, Di, and ai are introduced intrinsic parameters that are parameters of nonanalytic terms, which are included in nonlinear fitting of the whole equation, and θ is an adjustable parameter function;
Step 9:
calculating an enthalpy value according to the following formula:
h
=
u
+
pv
(
10
)
h
⁡
(
δ
,
τ
)
RT
=
1
+
τ
⁡
(
ϕ
τ
°
+
ϕ
τ
r
)
+
δ
⁢
ϕ
δ
r
(
11
)
ϕ
τ
°
=
[
∂
ϕ°
∂
τ
]
δ
,
ϕ
τ
r
=
[
∂
ϕ
r
∂
τ
]
δ
,
and
⁢
ϕ
δ
r
=
[
∂
ϕ
r
∂
δ
]
τ
(
12
)
wherein h is the enthalpy value, u is system inner energy, p is an external pressure, v is a system volume,
ϕ
τ
∘
is a first derivative of ϕ° with respect to τ,
ϕ
τ
r
is a first derivative of ϕr with respect to τ, and
ϕ
δ
r
is a first derivative of ϕr with respect to δ;
Step 10:
assuming 3He/enthalpy ratios of mantle and crust thermal endmembers and estimating heat contributions of the mantle and the crust to a basin geothermal system according to a heat balance equation;
(3He/enthalpy)calculated=XM(3He/enthalpy)mantle+(1−XM)(3He/enthalpy)crust (13)
wherein XM is a mantle heat fraction in the sample, (3He/enthalpy)calculated is a 3He/enthalpy ratio calculated according to the formula (1), and (3He/enthalpy)mantle and (3He/enthalpy)crust respectively represent 3He/enthalpy ratios of mantle and crust thermal endmembers;
Step 11:
determining a calculated mantle heat fraction as the relative heat contribution of the mantle to the basin geothermal system, the remaining contribution to the basin geothermal system coming from crust, a sum of contribution proportions of the two sources being 100%, the calculated mantle heat fraction indicating the contribution proportion of the mantle, and the remaining proportion indicating the contribution proportion of the crust;
and
Step 12:
optimizing a drilling path based on results of the evaluation method for relative contributions of heat sources based on helium which provides a reliable resource exploitation and reduces exploration risks.

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Evaluation method for relative contributions of heat sources based on helium and application thereof

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Evaluation method for relative contributions of heat sources based on helium and application thereof

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Abstract

Claims3