US 11,441,986 B1 · Disturbance and stability analysis method for hydrate reservoirs with difference buried depths

Abstract

The present invention relates to disturbance on hydrate reservoirs with different buried depths, in particularly to a disturbance and stability analysis method for hydrate reservoirs with different buried depths. Preparing a series of stable hydrate systems parallel to a hydrate phase equilibrium curve, wherein both of the porosities and the hydrate saturations of various hydrate systems are consistent, but the buried depths are different; disturbing the series of hydrate systems prepared in the first step, conducting disturbance under different conditions aiming to the hydrate systems with different buried depths; analyzing the stability of the hydrate reservoirs. By controlling the disturbance condition, the hydrate systems with different buried depths may be decomposed along the hydrate phase equilibrium curves thereof or in the hydrate unstable regions; and the decomposition productivity difference between the hydrate reservoirs with different buried depths may be intuitively and scientifically simulated and analyzed.

A disturbance and stability analysis method for hydrate reservoirs with different buried depths, comprising the following steps:

S1:
preparing a series of stable hydrate systems parallel to a hydrate phase equilibrium curve, wherein both of the porosities and the hydrate saturations of various hydrate systems are consistent, but the buried depths are different;
a temperature value and a pressure value of each stable hydrate system are Ti and Pi respectively, wherein i represents each of stable hydrate systems i with different buried depths;
and the corresponding temperature values and pressure values of the hydrate systems with different buried depths need to satisfy the following condition:
ln(Pi)=−1.9413850446456×105+3.31018213397926×103(Ti+Tt)−22.5540264493806(Ti+Tt)2+0.0767559117787059(Ti+Tt)3−1.30465829788791×10−4(Ti+Tt)4+8.86065316687571×10−8(Ti+Tt)5,
wherein Tt is a specified numerical value with the unit of ° C.;
S2:
disturbing the series of hydrate systems prepared in the first step, conducting disturbance under different conditions aiming to the hydrate systems with different buried depths, and monitoring and collecting the gas production rates Vg and the water production rates Mw of the systems under disturbance;
S3:
analyzing the stability of the hydrate reservoirs with different buried depths based on real-time variable quantities of the gas production rates Vg and the water production rates Mw;
in the step S1, the preparation process of the stable hydrate systems comprises the following steps:
S1.1:
filling a cleaned and dried reaction kettle with a known volume Vhf with sediment with a known density, compacting the sediment, recording a weight of the filled sediment, and covering the reaction kettle with a kettle cover;
after purging with methane gas for several times, continuously injecting pure methane gas;
controlling the content of the methane gas entering the reaction kettle with a gas flowmeter at VCH4, and at this time, obtaining the quantity of the methane gas substance injected into the system:
nCH4=VCH4/22.4;
closing an injection valve of the reaction kettle, setting a temperature of a system as the room temperature, and waiting for the system to be stabilized;
and when preparing the hydrate systems with different buried depths, enabling the injection quantities of the sediment and the injection quantities of the methane gas to be the same, wherein the unit of VCH4 is mL, and the unit of nCH4 is mol;
S1.2:
opening the injection valve again, and injecting deionized water into the reaction kettle with the injection quantity of Vwi the injection quantities of the deionized water for the hydrate systems with different buried depths are different, and with increase in buried depth of the hydrate systems, the injection quantity of the deionized water is increased;
after closing the valve and waiting for the system to be stabilized, cooling the reaction kettle to 0.5° C.;
and after hydrates are synthesized and the hydrate systems are finally stabilized, recording an average temperature Thdi and a pressure Phdi of each system at this time, wherein the unit of Thdi is ° C., the unit of Phdi is MPa and the unit of Vwi is mL;
wherein a measuring standard of the injection quantity Vwi of the deionized water is
V
wi
18
≥
6
⁢
n
C
⁢
H
4
,
and the system pressure condition Phdi>Pei is guaranteed with the injection quantity after the hydrates are synthesized, wherein Pei is a corresponding hydrate phase equilibrium pressure at the system average temperature Thdi, and a calculating formula of Pei is as follows:
ln(Pei)=a0++a2T2+a3T3+a4T4+a5T5, (1)
wherein T=Thdi+273.15, the unit of T is K;
and a0-a5 take values under the following conditions:
{
a
0
=
-
1.9413850446456
×
10
5
a
1
=
3.31018213397926
×
10
3
a
2
=
-
2.25540264493806
×
10
1
a
3
=
7.67559117787059
×
10
-
2
a
4
=
-
1.30465829788791
×
10
-
4
a
5
=
8.86065316687571
×
10
-
8
⁢
0
⁢
°
⁢
C
.
≤
T
hdi
≤
25
⁢
°
⁢
C
.
,
{
a
0
=
-
4.38921173434628
×
10
1
a
1
=
7.76302133739303
×
10
-
1
a
2
=
-
7.27291427030502
×
10
-
3
a
3
=
3.85413985900724
×
10
-
5
a
4
=
-
1.03669656828834
×
10
-
7
a
5
=
1.09882180475307
×
10
-
10
-
25
⁢
°
⁢
C
.
≤
T
hdi
≤
0
⁢
°
⁢
C
.
S1.3:
through the formula (1), reversely solving a corresponding equilibrium temperature Tei at a system stabilization pressure Phdi, slowly raising the temperature of each system to (Tei−Tt) at a rate of 1/4-2° C./h;
wherein Tt is a specific numerical value, and Tt<Tei;
and at this time, a final average temperature of the hydrate systems with different buried depths is Ti=Tendi=Tei−Tt, and the pressure is Pi=Phdi.

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Disturbance and stability analysis method for hydrate reservoirs with difference buried depths

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Disturbance and stability analysis method for hydrate reservoirs with difference buried depths

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Abstract

Claims6