US 12,163,905 B2 · Method for determining phase-state type and saturation of fluid in tight reservoirs by NMR technology

Abstract

A method for determining a phase-state type and saturation of a fluid by an NMR technology includes putting a core to be measured to an NMR phase-state testing device, injecting a heavy water solution from both ends of a gripper at the same time until the core reaches the formation pressure, and stopping; scanning the core to obtain a two-dimensional NMR map, and determining whether the core contains a gas phase; reducing the temperature of the gripper, and collecting an oil phase volume, a gas phase volume and a water phase volume discharged from the core; purge the pipelines out with nitrogen, collecting a water phase volume and an oil phase volume in the pipelines; performing dry distillation on the core to obtain an oil phase volume and a water phase volume; and obtaining the saturations of various phases according to the fluid volumes of multiple phases in the core.

A method for determining a phase-state type and saturation of a fluid in tight reservoirs by an NMR technology, comprising the following steps in sequence:

(1) drilling a 1-inch columnar core to be measured in an axial direction at the center of a frozen core, and continuously pouring liquid nitrogen into the core to be measured to prevent the fluid from heat loss;
(2) preparing a PTFE pipe with the same size as the core to be measured, sleeving the core to be measured with the PTFE pipe, sealing both ends of the pipe, and putting the pipe in the liquid nitrogen for freezing;
(3) putting the core to be measured, sleeved with the PTFE pipe, into a gripper, and putting the gripper into an NMR phase-state testing device, wherein the device is provided with a high-temperature circulating system, and a pressure gauge, a valve and a heavy water solution intermediate container are respectively connected to both ends of the gripper through pipelines;
a total volume of the pipelines of the device is Vi;
dead volumes of the pipelines and valves are filled with a prepared heavy water solution, and the gripper installation and pipeline connection are completed at the time when the nitrogen is completely evaporated with reference to a liquid nitrogen volatilization relationship diagram of the core;
(4) turning on the high-temperature circulating system to heat the gripper and gradually raising a core temperature;
if the core does not restore to a formation pressure after the core restores to a formation temperature, injecting the heavy water solution from both ends of the gripper at the same time until the core reaches the formation pressure, and stopping;
recording a volume ViD of the heavy water solution entering the gripper;
if the core has restored to the formation pressure, proceeding directly to the next step;
(5) scanning the core by NMR to obtain a T1-T2 two-dimensional NMR map;
(6) reducing the temperature of the gripper, reducing the pressure after returning to room temperature, and collecting an oil phase volume Vdo, a gas phase volume Vdg and a water phase volume VdD discharged from the core during the pressure reduction process;
(7) blowing liquid in the pipelines out with nitrogen, collecting a water phase volume VtD and an oil phase volume Vto in the pipelines blown out by the nitrogen, and calculating a gas phase volume Vtg in the pipelines according to a formula (1):
V
t
=
V
tD
+
V
to
+
V
tg
(
1
)
(8) calculating the volume VCD of the heavy water solution injected into the core:
V
o
=
(
V
do
+
V
to
+
V
ro
)
*
B
o
(
3
)
V
w
=
(
V
rw
-
V
CD
)
*
B
w
(
4
)
in which, ViD is the volume of the heavy water solution injected into the gripper in the process of restoring to the formation pressure;
and BD is a volume coefficient of the heavy water solution;
(9) removing the core from the gripper for rock pyrolysis;
setting an oil phase volume of Vro after rock pyrolysis, and a water phase volume of Vrw after rock pyrolysis;
and calculating an oil phase volume Vo and a water phase volume Vw of the core under the formation conditions, respectively:
V
CD
=
V
iD
+
⁢
V
t
B
D
-
V
dD
-
V
tD
(
2
)
in which, Vdo is the oil phase volume discharged from the core during the pressure reduction process;
Vto is an oil phase volume blown out from the pipelines with nitrogen;
Vro is an oil phase volume obtained by dry distillation;
Bo is a crude oil volume coefficient;
Vrw is a water phase volume obtained by dry distillation;
VcD is a volume of the heavy water solution injected into the core;
and Bw is a formation water volume coefficient;
(10) determining whether the core contains a gas phase in its original state according to the T1-T2 two-dimensional NMR map, wherein the core contains oil-water two-phase fluid if there is no gas phase inside, and the core contains oil-water-gas three-phase fluid if there is a gas phase inside;
and calculating a gas phase volume Vg in the core under the formation conditions according to the following formula:
V
g
=
(
V
dg
+
V
tg
)
*
B
g
(
5
)
in which, Bg is a formation gas volume coefficient;
and
(11) obtaining the saturations of various phases respectively under the original conditions according to the calculated fluid volumes of multiple phases in the core under the formation conditions.

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Method for determining phase-state type and saturation of fluid in tight reservoirs by NMR technology

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Method for determining phase-state type and saturation of fluid in tight reservoirs by NMR technology

Life of this patent

Abstract

Claims5