Special Oil & Gas Reservoirs >

2021 , Vol. 28 >Issue 1: 118 - 124

DOI: https://doi.org/10.3969/j.issn.1006-6535.2021.01.017

Reservoir Engineering

Study on Seepage Characteristics of Fluid Between Matrix and Fracture in CO2 Huff-puff Process in Fractured Tight Reservoirs

  • Gong Lianhao ,
  • Liu Jizi ,
  • Wu Xing ,
  • Bu Guangping ,
  • Huang Fan ,
  • Yang Long
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  • PetroChina Changqing Oilfield Company, Yulin, Shaanxi 718606, China

Received date: 2020-03-07

  Revised date: 2020-11-01

  Online published: 2021-04-27

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Abstract

In order to further explore the seepage mechanism of fluid between matrix and fracture in CO2 huff-puff process in fractured tight reservoirs, a self-designed high-pressure non-magnetic core holder was used to perform pulsed CO2 huff-puff core experiment. Based on the principle of nuclear magnetic resonance T2 spectrum testing, the core was scanned online in the process of CO2 huff and puff to study the micro production characteristics of crude oil in the pores of matrix and the seepage characteristics of fluid between matrix and fracture during CO2 huff and puff. he results of the study show that after CO2 entered the fracture, the crude oil was displaced along the fracture, but the crude oil in the matrix could not be produced. At the early stage of well shut-in, the crude oil saturated with CO2 in the matrix macropores (20.5 ms ＜ T2 ≤ 716.0 ms) entered the fractures under the action of expansion. At the later stage of the shut-in, the differential diffusion of crude oil concentration caused by CO2 extraction and the capillary force of pores in different sizes gradually became the the dominant force, and prolongation of shut-in time could effectively increase the production degree of crude oil in the matrix. The recovery efficiency of crude oil was main contributed by the large pores, while the production degree of small pores was poor. With the increase in the pulsed gas injection cycle, the cyclic matrix recovery percent was continuously reduced. The CO2 huff-puff cycle should be reduced and the shut-in time should be prolonged during the implementation at the mine. In addition, the lower limit of depletion pressure should be set close tot he saturation pressure to improve the overall recovery efficiency during huff and puff. The study results provide reference and basis for enhancing the recovery efficiency of fractured tight oil reservoirs.

Key words： tight oil reservoir; nuclear magnetic resonance; CO2 huff-puff; matrix-fracture; micro-pore; seepage characteristics

Cite this article

Gong Lianhao , Liu Jizi , Wu Xing , Bu Guangping , Huang Fan , Yang Long . Study on Seepage Characteristics of Fluid Between Matrix and Fracture in CO2 Huff-puff Process in Fractured Tight Reservoirs[J]. Special Oil & Gas Reservoirs, 2021 , 28(1) : 118 -124 . DOI: 10.3969/j.issn.1006-6535.2021.01.017

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