Title: Visualisation and investigation of water retention in tight oil reservoir via real sandstone micro-models

Authors: Yafei Liu; Yuhan Shi; Haien Yang; Tianjiang Wu; Xiong Liu; Shun Liu; Desheng Zhou

Addresses: Shaanxi Key Laboratory of Advanced Stimulation Technology for Oil and Gas Reservoirs, Xi'an Shiyou University, Xi'an, Shaanxi, China; Ministry of Education, Engineering Research Center of Western Low and Ultralow Permeability Oilfield Development and Management, Xi'an Shiyou University, Xi'an, Shaanxi, China ' PetroChina Changqing Oilfield Company, No. 6 Gas Production Plant, Xi'an Shaanxi, China ' Oil and Gas Technology Research Institute, Changqing Oilfield Company, PetroChina, Xi'an, Shaanxi, China; National Engineering Laboratory of Low Permeability Oil and Gas Field Exploratory and Development, Xi'an, Shaanxi, China ' Oil and Gas Technology Research Institute, Changqing Oilfield Company, PetroChina, Xi'an, Shaanxi, China; National Engineering Laboratory of Low Permeability Oil and Gas Field Exploratory and Development, Xi'an, Shaanxi, China ' Shaanxi Key Laboratory of Advanced Stimulation Technology for Oil and Gas Reservoirs, Xi'an Shiyou University, Xi'an, Shaanxi, China; Ministry of Education, Engineering Research Center of Western Low and Ultralow Permeability Oilfield Development and Management, Xi'an Shiyou University, Xi'an, Shaanxi, China ' Shaanxi Key Laboratory of Advanced Stimulation Technology for Oil and Gas Reservoirs, Xi'an Shiyou University, Xi'an, Shaanxi, China; Ministry of Education, Engineering Research Center of Western Low and Ultralow Permeability Oilfield Development and Management, Xi'an Shiyou University, Xi'an, Shaanxi, China ' Shaanxi Key Laboratory of Advanced Stimulation Technology for Oil and Gas Reservoirs, Xi'an Shiyou University, Xi'an, Shaanxi, China; Ministry of Education, Engineering Research Center of Western Low and Ultralow Permeability Oilfield Development and Management, Xi'an Shiyou University, Xi'an, Shaanxi, China

Abstract: Hydraulic fracturing is considered as an effective approach for the development of tight oil reservoirs. Unlike conventional reservoirs, after a large volume injection of the fracturing fluid, the flowback rate in tight oil reservoirs is considerably lower whereas the underlying mechanism explaining water retention remains unclear. Therefore, in this work, to investigate the water retention mechanism, fracturing fluid injection and particularly oil production process were emulated within real tight rock chips. Displacement and water retention events were directly visualised and captured using a microscope. As a result, the discrepancy between temporary and permanent residence of water inside the pore space was clarified. Additionally, nuclear magnetic resonance (NMR) scanning was incorporated to study the pore-scale fluid flow behaviours. Results show that a large portion of water was retained in smaller pores and water retention rate is positively correlated with oil recovery, implying invaded water replaced the oil and resided in the pore space therefore increasing the mobile oil in the formation as oil flowing back. This work proposed an interpretation of water retention mechanism in tight oil reservoir after hydraulic fracturing and provided an insight to optimise the development and production of tight oil reservoirs. [Received: January 20, 2020; Accepted: April 23, 2020]

Keywords: hydraulic fracturing; water retention; tight oil reservoir.

DOI: 10.1504/IJOGCT.2021.115542

International Journal of Oil, Gas and Coal Technology, 2021 Vol.27 No.2, pp.111 - 126

Received: 20 Jan 2020
Accepted: 23 Apr 2020

Published online: 01 Jun 2021 *

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