Redevelopment potential of NNW oil field, Ordos Basin—an analysis

doi:10.13745/j.esf.sf.2022.8.34

Abstract

Abstract:

The main producing zones of NNW oil field, Ordos Basin, are the Chang 6 and Chang 4+5 members of the Triassic Yanchang Formation, which consist numerous amalgamated lenticular and some sheet sands of fluvial and lacustrine deltaic facies and are classified as unconventional tight sand reservoirs. Past well completion was geared toward completing only a single pay sand in each well, however, such insufficient reservoir opening greatly suppressed daily production rate. Through modeling using an elliptoconic drainage model we found there is still a large quantity of oil left between the existing vertical wells that have a drainage radius seldom beyond 50 m. We propose to replace the single pay mining practice with multistage fracking aiming toward completing all pay sands simultaneously. We further suggest that oil field redevelopment using horizontal wells presents the most important future development opportunity, as horizontal drilling and multistage fracking has the potential to multiply oil field production and economic profit. According to our analysis the NNW oil field has sufficient resource base for redevelopment.

Key words: ultra-low permeability, elliptical cone, multistage fracture, horizontal well

CLC Number:

P618.13

HU Guonong, HAO Shiyan, FAN Pingtian, LI Yu, GAO Qinghua. Redevelopment potential of NNW oil field, Ordos Basin—an analysis[J]. Earth Science Frontiers, 2023, 30(1): 106-115.

Figures/Tables 14

Fig.1 Oil saturation distribution of Chang 6 Reservoir, XY area, through 3D geological modeling

Fig.2 Perforation thickness distribution among XY,Y885 and N199 areas (based on 940 production wells)

Fig.3 In-place reserves per unit area (m3/m2) of the four reservoir subgroups in the XY area(The grid in the map is 500 m×500 m)

Fig.4 In place reserves per unit area (m3/m2) of the four reservoir subgroups in the Y885 area(The grid in the map is 500 m×500 m)

Fig.5 In place reserves per unit area (m3/m2) of the four reservoir subgroups in the N199 area(The grid in the map is 500 m×500 m)

Fig.6 Elliptoconic drainage model for a hydraulically fractured well

Fig.7 Elliptoconic drainage modeling results of a small region in XY area

Fig.8 Remaining in-place reserves per 100 m2 area (m3/100 m2) in XY area (The grid in the map is 500 m×500 m)

Fig.9 Remaining in-place reserves per 100 m2 area (m3/100 m2) in Y885 area (The grid in the map is 500 m×500 m)

Fig.10 Remaining in-place reserves per 100 m2 area (m3/100 m2) in N199 area (The grid in the map is 500 m×500 m)

Fig.11 Frac parameters used in old vertical wells within the study area (based on 1348 fracs)

Fig.12 Example of redevelopment of old field with horizontal wells, Wattenberg Field, Denver Basin, USA

Fig.13 History of monthly production from Horizontal wells, Wattenberg Field (Based on 3880 HZ producers)

Fig.14 Monthly production decline curve (initial production time normalized) comparison between vertical (4458 wells) and horizontal wells (3880 wells), Wattenberg Field

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