Well path design by integrating the analysis of wireline logs and the interpretation of seismic data for a fractured basement reservoir in Cuu Long Basin, Viet Nam

The BZ19‐6 structural belt is the largest buried hill oil‐gas‐bearing area recently discovered in Bohai Bay Basin. The formation and evolution of the buried hill reservoirs are complex. Presently, the development law and controlling factors of this reservoir is unclear. Based on 3D seismic, drilling data, thin section, and regional tectonic background, we explored the controlling factors and development law of the high‐quality buried hill reservoir. The results show that the buried hill reservoir can be vertically divided into a weathered glutenite zone, weathered fracture zone, internal fracture zone, and tight zone. The development of reservoir is mainly controlled by lithotypes, tectonic movement, and weathering. The rocks in the study area with low compressive strength, provided the material basis for the formation of fractures. The strongly reformed multi‐stage tectonic movements provides the external dynamics for the formation of fractures. Weathering further improved the physical properties of the reservoir. The buried hill reservoir is mainly distributed in the weathered fracture zone and internal fracture zone. Currently, natural gas mainly found in nearly E‐W‐trending and N‐S‐trending fractures. The nearly E‐W‐trending fractures are developed in the thrust nappe structure formed by N‐S‐trending extrusion in the Indosinian. The hinge zone of the structure is the main development area of fractures. The nearly N‐S‐trending fractures are associated with strike‐slip faults formed by sinistral strike‐slip stress in the Yanshanian. Under the background of NNE–SSW direction extensional stress during the Himalayan, early fractures were reactivated, opened and expanded, forming the reservoir space for later natural gas charging.

Section: Introductionmentioning

confidence: 99%

Formation mechanism and evolution model of buried hill reservoir in BZ19‐6 structural belt, Bozhong Sag, Bohai Bay, East China

Shi,

Xie,

et al. 2023

“…Granite can form a high‐quality reservoir for a large number of secondary reservoir spaces developed during the processes of the weathering, leaching, and multi‐phase tectonic activities (Louis, Vincent, & Tammy, 2018; Wang, Wang, Liu, Zhao, & Hao, 2019; Yu et al, 2019). Some large‐scale oil fields have been explored in granitic buried hills worldwide, such as the Bach Ho oilfield, oil reservoirs in Precambrian basement in Gulf of Suez Basin and granitic gneiss in Sousa Basin (Carvalho, Mendes, & Costa, 2013; Cuong & Warren, 2009; Guo et al, 2017; Hu, Xu, Yang, Huang, & Su, 2017; Nguyena, Hwang, Jang, Hoang, & Pham, 2018; Salah & Alsharhan, 1998). The dissolution pore, broken inter‐granular pore, dissolution fracture, and the structural fracture constitute the various reservoir spaces (Carvalho et al, 2013; Cuong & Warren, 2009; Salah & Alsharhan, 1998; Adelu et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Characteristics and vertical zonation of large‐scale granitic reservoirs, a case study from Penglai oil field in the Bohai Bay Basin, North China

Chen

Niu

et al. 2020

Primary pores are undeveloped in the granite, but multiple types of reservoir spaces can form during the processes of weathering and tectonic movement. Taking Penglai (PL) oil field as an example, the vertical zonal characteristic of the buried granite is defined and the relationship between different zones and reservoir is discussed. The granite can be divided into weathered zone (WZ) and bedrock zone (BZ) vertically according to weathered or not, and the WZ can be divided into weathered clay zone (WCZ), weathered glutenite zone (WGZ), and weathered fracture zone (WFZ) further. The lithology, mineral composition, and weathering indices (geochemistry) can distinguish different zones. Both WZ and BZ can form good reservoirs, among them the reservoir of WGZ is dominated by pores, while that of WFZ and the BZ are mainly composed of fractures, and they constitute the high-quality reservoir together. There is an obvious positive correlation between the thickness of fracture zone in BZ and the thickness of WZ, and both WZ and BZ are influenced by tectonic movement. Moreover, WZ superimposed with meteoric water dissolution makes it the best reservoir in the granitic buried hill, and the development of fractures in BZ extends the thickness of reservoir greatly.

“…Buried hills are topographic highs on old land surfaces which are reflected in the superposed sedimentary deposits (Powers, 1926). Buried hill reservoirs, or oil and gas accumulations associated with buried hills, were first discovered in the early 1900s (Landes, Amoruso, Charlesworth, Heany, & Lesperance, 1960; Nguyen, Hwang, Jang, Hoang, & Pham, 2018; Sircar, 2004). After the excavation of the buried hill in the Healdton oil field (Oklahoma, USA) in 1916, more buried hills were identified in other parts of the world (Dake & Bridge, 1932).…”

Section: Introductionmentioning

confidence: 99%

Characteristics and formation mechanism of the fractures in Archaean buried hill: A case study in the BZ19‐6 Block, Bohai Bay Basin, China

Dai

Tang

Li³

et al. 2020

While Archean buried hill fractured reservoirs have been found for the first time in the BZ19‐6 Block of the Bozhong Sag in the Bohai Bay Basin, the mechanisms driving their creation and evolution are not well known for low degree of exploration. Using core data, image logs, and our knowledge of the regional geology, we characterized the features and explored the formation mechanisms of these fractures. Our core samples captured two types of fractures: high‐angle shear fractures and low‐ to moderate‐angle tensile fractures. Based on the cross‐cutting relationships, four distinct sets of fractures formed at different stages and related to different tectonic events. The first fracture set (Set I) is high‐angle shear fractures having an E‐W orientation, partially filled by calcite, and was formed by transpressive processes in the Early Yanshanian. The second fracture set (Set II) is characterized by moderate angles, partially filled by asphalt and calcite with variable orientations and a more mesh‐like appearance, formed in an extensional environment in the middle Yanshanian. During transpressive activities in the Late Yanshanian, the high‐angle shear fractures of the third fracture set (Set III) formed with NW‐SE orientations and partially filled by asphalt. The fourth fracture set (Set IV), which occurred in the Early Himalayan, involves high‐angle shear fractures that is oriented in the NE‐SW direction and only part of them are filled by clay minerals. Macroscopic fracture features, orientations, and distribution patterns can significantly alter the nature of a reservoir; the fractures in Set I (E‐W‐oriented) and III (NW‐SE‐oriented) are typically the widest (excluded fills), and they tend to have the greatest impact on the overall reservoir permeability.