Novel Insights into the Movable Fluid Distribution in Tight Sandstones Using Nuclear Magnetic Resonance and Rate-Control
- PDF / 1,638,394 Bytes
- 11 Pages / 595.276 x 790.866 pts Page_size
- 56 Downloads / 207 Views
Original Paper
Novel Insights into the Movable Fluid Distribution in Tight Sandstones Using Nuclear Magnetic Resonance and Rate-Controlled Porosimetry Fuyong Wang
1,2
and Fanchao Zeng1 Received 5 November 2019; accepted 7 February 2020
To characterize the movable fluid distribution in tight sandstones and determine its influencing factors, 20 tight sandstone core samples from the Chang-6 and Chang-8 Members of the Yanchang Formation in the Ordos Basin, NW China, were analyzed using nuclear magnetic resonance (NMR) and rate-controlled porosimetry (RCP). The conventional method of movable fluid analysis divides the whole NMR T2 spectrum into two parts, namely unmovable and movable fluids, based on a single T2cutoff value. However, this conventional method ignores pore size wherein fluid is partially movable. In this paper, the fluid in tight sandstones is divided into three parts, i.e., completely unmovable, partially movable and completely movable fluids. Based on the throat size distribution obtained from RCP, T2 spectra were converted into corresponding pore-throat sizes with the nonlinear conversion method, and then the critical pore-throat sizes for fluid distribution were derived. The research results show that the average residual liquid saturation was 46.14% under a centrifugal pressure of 900 psi. On average, the completely unmovable fluid occupied approximately 18% of the total pore volume of tight sandstones, the partially movable fluid accounted for approximately 72% of the total pore volume, and the completely movable fluid accounted for only approximately 10% of the total pore volume. The pore throats filled with completely unmovable fluid contributed very little to the permeability. Compared with the Chang-8 Member, the tight sandstones of the Chang-6 Member had higher completely unmovable fluid saturation and larger critical pore-throat size of the completely unmovable fluid. KEY WORDS: Tight sandstone, Movable fluid, Nuclear magnetic resonance, Rate-controlled porosimetry, Throat radius, T2 spectra.
INTRODUCTION Tight oil is a kind of unconventional oil resource and cannot be produced feasibly with standard drilling techniques due to its ultra-low permeability and porosity; the matrix porosity is 1
Unconventional Petroleum Research Institute, China University of Petroleum, Beijing 102249, PeopleÕs Republic of China. 2 To whom correspondence should be addressed; e-mail: [email protected]
usually lower than 10%, and the permeability with the overburden pressure is no higher than 0.1 mD (Jia et al. 2012; Zhu et al. 2019). Effective development of tight oil is of great significance for the energy supply and economic development (Zou et al. 2014; Zhu et al. 2019). The tight oil and gas reserves in the Ordos Basin, NW China, are abundant. The Ordos Basin is located in North-Central China, and the Upper Triassic Yanchang Formation is divided into 10 members, from Chang-1 to Chang-
Ó 2020 International Association for Mathematical Geosciences
Wang and Zeng Table 1. Parameters of the tight sandst
Data Loading...
