Evaluation of seismic and petrophysical parameters for hydrocarbon prospecting of G-field, Niger Delta, Nigeria

Journal of Petroleum Exploration and Production Technology https://doi.org/10.1007/s13202-019-0735-5 ORIGINAL PAPER - EXPLORATION GEOPHYSICS Evaluation of seismic and petrophysical parameters for hydrocarbon prospecting of G‑field, Niger Delta, Nigeria Anthony Aduojo Ameloko1 · George Chiemeziem Uhegbu1 · Eniola Bolujo1 Received: 15 February 2019 / Accepted: 16 July 2019 © The Author(s) 2019 Abstract Adequate analyses of seismic and petrophysical data help to minimize drilling risk and maximize well and reservoir productivity. Reservoir characterization was carried out to provide information and improve understanding of the geological and petrophysical parameters, and hence improve decision making regarding the development of the field under study. Wireline logs obtained from three wells as well as a 3D Seismic data coverage of G-field in the Niger Delta were evaluated using the petrel software. Suites of gamma and deep resistivity logs aided the delineation and correlation of the sandstone unit, while the top was tied to the seismic data using synthetic seismogram to determine seismic characters. Well correlation enabled the delineation of reservoir sand across the wells. The quality of the reservoir was determined from petrophysical averages, in which the reservoir has an average thickness of 72 m, average porosity of 0.31, average net to gross of 0.75, average V-shale of 0.25, and average water saturation of 0.19, respectively. Listric normal faults were mapped across the field. The models reveal lateral and horizontal variations in reservoir properties which capture subsurface heterogeneity and anisotropy across the reservoir sand, and also possible sweet-spot zones were identified. These are diagnostic of areas for future exploitation and recovery of hydrocarbon. Seismic attributes analysis was done to predict variation in lithofacies across the sandstone body. Keywords Reservoir · Seismic · Logs · Porosity · Faults Introduction Many dry holes have been drilled in the Niger Delta as a result of inaccurate analysis of the integrity of the numerous fault-dependent closures and stratigraphic setting associated with the basin. The Niger Delta like many deltaic areas is extremely difficult to define due to the heterogeneous nature of the various sedimentary lithofacies units associated with it. This complex physical property of the basin has made it extremely difficult to define formations and their interfaces. And so integration of 3D seismic and well data for structural interpretation and reservoir characterization is a continuous process of providing an improved understanding of the geological and petrophysical controls of fluid flows in the reservoir. It encompasses all methods and techniques that can lead to a well-improved understanding and a much better handling of the reservoir. Reservoir characterization * Anthony Aduojo Ameloko 1 Department of Petroleum Engineering, Covenant University, Ota, Nigeria is defined as a systematic means of quantitatively determining and assigning reservoir properties, establishing geologic information and uncertainty in spatial variability (Lake and Carroll 1986). Subsurface configurations must be well understood in order to be able to efficiently delineate the structures that are favorable for the accumulation of hydrocarbon; and several geologic parameters are important accumulation, gas and oil in large quantities, to form a pool sufficient enough for production. These parameters include good source rock (an organic-rich) to produce the oil or gas, a reservoir rock with sufficient porosity to accommodate the hydrocarbon, and good structural framework to prevent the oil and gas from leaking away (Coffen 1984). The importance of data integration is usually in improvement in the accuracy of mapping complicated structural plays (Adejobi and Olayinka 1997). When 3D seismic data are interpreted and made clear with modern computer workstations and software for interpretation, structural mapping can be done swiftly and accurately. However, it is not enough just to map the top of the reservoir (as was the case in two dimensions). To understand how structures were formed and when, it is usually necessary to map a range of marker horizons above 13 Vol.:(0123456789) Journal of Petroleum Exploration and Production Technology and below the target. This study therefore was aimed at integrating well and seismic data obtained from the field under study, to effectively characterize subsurface sandstone reservoir and evaluate its hydrocarbon potentials. of alluvial sands and characterized by thicknesses of about 2000 m (Avbovbo 1978) (Fig. 1). Materials and methods Location and geology of the study area Seismic and well log data analyses The G-field is located in the Niger Delta basin in Nigeria (Fig. 2). The basin is characteristically a clastic wedgeshaped structure located along a failed arm of a triple junction framework (aulacogen) initially developed as a result of the separation of the South American and African plates during the late Jurassic time (Burke 1972; Whiteman 1982). The two arms are associated with the southwestern and southeastern coast of Nigeria and Cameroon formed into the passive continental margin of West Africa, while the third failed arm formed the Benue Trough. The sub-areal bit of the Niger Delta covers around 75,000 km2 territory inside the Gulf of Guinea and extending more than 300 km from summit to mouth. In spite of the way that the progressed Niger Delta shaped in the early tertiary, residue began to accumulate in this area in the midst of Mesozoic breaking associated with the partition of the African and South American landmasses (Doust and Omatsola 1990; Evamy et al. 1978; Weber and Daukoru 1975). Like many deltaic areas, the Niger Delta is complex and it is difficult to determine a satisfactory stratigraphic signature. The improper alignment of a small number of lithofacies makes it difficult to establish units and boundaries of sufficient integrity to constitute separate formations in a formal sense. However, three formation names are in widespread use corresponding to the portions of the tripartite sequence previously described (Avbovbo 1978; Short and Stauble 1967). In the Nigerian oil industry, these three are usually referred to in the lithofacies terms. The Niger Delta basin is divided into three main formations: Akata, Agbada and the Benin Formations. The oldest of them is the Akata Formation, which is made up of thick sequences of shale and it is regarded as the source rock for hydrocarbon formation. The origin of this important unit of the basin is related to the transportation of terrestrial organic matter and clays to deep offshore waters at the beginning of Paleocene (Tuttle et al. 1990). According to Doust and Omatsola (1990), the formation is estimated to be about 7000 m thick, and underlies the entire delta with high overpressure. The Agbada Formation directly overlies the Akata (...truncated)