Wireline Log Interpretation Research Articles

Investigation of Source and Reservoir Rock Petroleum Generative Potential of Early Eocene and Paleocene Sequences of the Punjab Platform Basin, Pakistan: A Geochemical and Petrophysical Approach

Abstract ––Investigating Early Eocene and Paleocene deposits within the Punjab Platform, Pakistan, involved comprehensive analysis using advanced geochemical and petrophysical techniques. This study evaluates the source potential of three formations: Nammal and Sakesar of Early Eocene age and Dungan and Ranikot of Palaeocene age. The Sakesar Formation, a reservoir rock, was evaluated through interpretation of wireline logs to estimate key petrophysical properties—porosity, water saturation, and hydrocarbon saturation. Geochemical investigations focused on total organic carbon content and Rock-Eval pyrolysis of twenty-one cutting samples from a well. These samples displayed TOC values ranging from 0.21 to 2.04 wt.% and S2 values ranging from 0.09 to 2.14 mg HC/g rock. Analysis positioned all samples within the immature window zone with Type II/III and Type III kerogen, suggesting limited generative potential. Findings suggest limited hydrocarbon generation from these formations. Petrophysical analysis indicated average porosity of 11.2%, water saturation of 32.58%, and hydrocarbon saturation of 67.42% for the Sakesar Formation, categorizing it as average to good reservoir potential. This study highlights complex geochemical and petrophysical characteristics of these formations. While Sakesar shows promising reservoir qualities, significant hydrocarbon generation potential from Nammal, Dungan, and Ranikot formations is constrained. Informed decision-making is crucial when considering these formations as hydrocarbon sources.

Sequence Stratigraphy, Sedimentology, and Reservoir Characteristics of the Middle Cretaceous Mishrif Formation, South Iraq

The Cenomanian–Early Turonian Mishrif Formation is a great contributor to oil production in Iraq. Integrating petrographic, mineralogical, and wireline logging data from 52 wells, this study provides an improved understanding of the sequence stratigraphy, depositional evolution, and reservoir characteristics of the Mishrif Formation in the Mesopotamian Basin, south Iraq. Five types of facies associations are classified: lagoon, shoal, rudist bioherm, shallow marine, and deep marine. Such a classification allows convenient differentiation and interpretation of wireline logs. A sequence stratigraphic framework including five third-order sequences (Mhf 1 to Mhf 5) for the Mishrif Formation is established mainly using wireline logging data of close-distance wells, with the aid of cores and thin sections. Two end-member depositional evolution stages are recognized, from clinoform-like progradational shoal complexes in Mhf 1 within a shallow marine environment, to tidal channels in Mhf 2–3 within a lagoon environment. For Mhf 4–5, abrupt changes in facies associations from north to south indicate the development of an intra-shelf basin where organic-rich mudstones directly overlie the shallow marine grainstone shoals and lagoonal wackestones. Reservoir characteristics and compartmentalization are directly controlled by the sequence stratigraphic framework. Sequence boundaries are featured by wackestones and mudstones overprinted by cementation; they are regionally correlatable and work as regional barriers. Shoal complexes in Mhf 1 and tidal channels in Mhf 2–3 are the main reservoir units. Mudstones and wackestones are intra-reservoir baffles and become more frequently developed towards the south, reflecting the increasing water depth towards south. The characterization of the tidal channels, clinoform-like shoals, and intrashelf basinal deposits in the current study could benefit later development of the Mishrif Formation.

Reservoir characterization, in relation to the petrophysical modeling of Baharyia formation, Razzak field, northern western desert, Egypt

The present work aims to investigate the reservoir characterizations of the Lower Cenomanian Baharyia Formation by creating isoparametic maps to calculate the petrophysical parameters and detect the favorable parts for oil accumulations using the available well logging data. Baharyia Formation is one of the main hydrocarbon sandstone reservoirs in the northern Western Desert of Egypt. About 90% of the Western Desert field produces form Baharyia sandstone Formation. This has been achieved through the analyses of the conventional wireline logs and petrophysical modeling. The Baharyia Formation comprises a complex of depositional lithofacies such as interbedded siltstone, shale, sandstones and pebbly sandstones. Petrophysical modeling of the Baharyia Formation was performed, based on the interpretation of complete wireline logs from five wells in Razzak oil field, north Western desert, Egypt. Petrophysical analysis accomplished, such as: shale volume, total and effective porosities, water saturation and hydrocarbon saturation, were deduced and utilized in the petrophysical subdivision of the Baharyia Formation. Relations between theses petrophysical parameters are established to define the implications of such parameters on the Baharyia Formation. Iso-parametric and litho-saturation crossplots are used to delineate variations in petrophysical parameters across the area. The obtained petrophysical results reveal that, the Baharyia Formation have a good reservoir quality, with high effective porosity values exceeding 18%,volume of shale about 30% and low water saturation values of 25%. The rock genetic types of the Baharyia Formation deduced form the log curve shapes proved that the Baharyia Formation was deposited from fluvial to marine environments passing through the tidal flood plain conditions. However, the lithology of the Baharyia Formation composed of sandstone, siltstone, shale and minor limestone inter-beds.

Cretaceous depositional environment interpretation of offshore Otway Basin cores and wireline logs; application to the generation of basin-scale gross depositional environment maps

Gas production from the Inner Otway Basin commenced in the early 2000s but the deep-water part of this basin remains an exploration frontier. Historically, the understanding of plays in this region were largely model driven and therefore the ground-truthing of depositional environments (DE) and gross depositional environments (GDE) are critical. This aspect has been investigated for the Sherbrook Supersequence (SS) by the integration of legacy wireline and core data, with regional 2D seismic facies mapping of new and reprocessed data from Geoscience Australia’s 2020 Otway Basin seismic program. Core observations were matched to wireline logs and seismic facies with resulting well-based DE interpretations calibrated to seismic resolution Regional GDE intervals. Integration of well and seismic observations led to the compilation of a basin-wide Regional GDE map for the Sherbrook SS. This GDE map indicates the distribution of Sherbrook SS play elements such as source rock, seal and reservoir, especially across the Deep-water Otway Basin where well data is sparse.

Petrophysical interpretation and reservoir characterisation on Proterozoic shales in National Drilling Initiative Carrara 1, Northern Territory

The Proterozoic succession in the National Drilling Initiative Carrara 1 drill hole, Northern Territory, is dominated by tight shales, siltstones and calcareous clastic rocks. As part of Geoscience Australia’s Exploring for the Future program, this study aimed to improve the Proterozoic shale gas reservoir characterisation by derivation of porosity, permeability and gas content from laboratory testing and machine learning approaches to wireline log interpretation. The Proterozoic Lawn Hill Formation is divided into four chemostratigraphic packages. The middle two packages are further divided into seven internal units according to principal component analysis and self-organising map clustering on well logs and inorganic geochemical properties. Artificial neural networks were then applied to interpret the mineral compositions, porosity and permeability from well logs, density and neutron-density crossplot interpretations. Gas content was estimated from the interpreted porosity, gas saturation, total organic carbon and clay contents. Petrophysical interpretation results are summarised for all chemostratigraphic packages and units. P2 (1126.3–1430.1 m) has the highest potential among the four chemostratigraphic packages. P2U1 (1126.3–1271 m) and P2U3 (1335.5–1430.1 m) units have the most favourable petrophysical properties for organic-rich shales, with average total gas contents of 1.213 and 1.315 cm3/g, geometric mean permeability of 6.6 and 25.31 µD and net shale thickness of 53.5 and 83.3 m, respectively. P3U4 (687.9–697.9 m) has high gas content and permeability, with a net shale thickness of 35.9 m. The tight non-organic-rich siltstone and shale reservoirs in package P1 (below 1430.1 m) have an average gas saturation of 17.4% and a geometric mean permeability of 0.48 µD.

Characterization and evolution of a carbonate basin floor fan on a leeward side of an isolated carbonate platform, Sirte Basin, Libya

The recognition of carbonate basin floor fans and the interpretation of their formation and evolution are extremely crucial to the hydrocarbon exploration since they form important oil and gas reservoirs. There has been little research on the geometries and controlling factors of the carbonate basin floor fans from subsurface three-dimensional (3D) seismic and wireline log data. Most studies have been conducted on siliciclastic basin floor fans. Thus, this study characterizes the internal configuration and processes controlling the deposition of a lower Eocene carbonate basin floor fan system in the Sirte Basin in a sequence stratigraphic context through integrated 3D seismic and wireline log interpretations. The carbonate fan complex shows hummocky to undulated seismic geometries on vertical seismic sections and bounded by an unconformable sequence boundary at the base and a downlap surface at the top. It has an aerial extension of around 9 km from south to north along depositional dip and at least 8 km from east to west along strike. In well data, the fan system predominantly comprises limestone units intercalated with thin shale intervals. Log curves display an overall funnel-shaped trend, suggesting progradational stacking pattern. The vertical thickness of the fan complex varies from 120 to 165 m. The evolution of the carbonate fan was influenced by the interplay of accommodation space and sediment supply. A pre-existing topography, tectonic subsidence, and sea-level rise generated accommodation space for the deposition of the fan system, whereas sediment-gravity flows transported the fan sediments from the platform interior and margin to the basin floor. This study provides sedimentological and stratigraphic criteria to recognize and interpret the evolution of basin floor fans along isolated carbonate platforms from 3D seismic and wireline log data and may serve as an analog for ongoing and future studies on carbonate basin floor fans elsewhere.

Prediction of Cretaceous reservoir zone through petrophysical modeling: Insights from Kadanwari gas field, Middle Indus Basin

This study involved an interpretation of wire-line logs in assessing the hydrocarbon capacity of the sandstone reservoir within the gas fields of Kadanwari, Sindh, Pakistan. Wire-line logs from four wells (KD-01, KD-03, KD-10 and KD-11) were used in our research and provided interpretation for thirteen reservoir zones. Reservoir analyses were done for effective porosity (ϕeff), shale content (Vsh), net pay thickness variations, water saturation, and hydrocarbon (Sw and Shc). Hydrocarbon-bearing zones consist of high values of resistivity, permeability, porosity, low water saturation content, and less shale content, indicating the presence of clean sand. The Thomas Stieber model findings show that in lower Goru sand, the laminated form of shale distribution persists. Sub-reservoirs’ petrophysical parameters were analyzed and ranked into a good sand reservoir quality (having ϕeff ∼0.11-0.44%), permeability (∼10.539-477.76 mD), hydrocarbon saturation (having Shc ∼0.59-0.86%), and water saturation (having Sw ∼0.18-0.45%). In the current research Indonesian model has been used to test for water saturation over a shaly-sand reservoir situated in a heterogeneous zone. It was observed that each well exhibited Sw at values lesser than 60%. This is indicative the selected zone has a hydrocarbon potential, and the hydrocarbons are of good quality. Isoparametric maps and crossplots of litho-saturation results reveal variations in the horizontal and vertical petrophysical parameters of the reservoir. The subsurface reservoir geographical distribution is visualized employing isoparametric maps. The fuel treasure in the southwestern section of the study area is enormous, as revealed by the petrophysical investigations, suggesting more well-drilling prospects in the gas fields of the lower Goru Formation situated in Kadanwari. Our research identified a quality hydrocarbon hotspot zone of immense economic value in Southern Kadanwari. In contrast, more research is needed regarding the northeastern section though our present findings suggest the northeastern section should be avoided because of excess shale and high-water concentrations.

Investigation on mechanism of low-resistivity oil reservoir in Minghuazhen and Guantao Formation of Nanpu Sag

Per the resistivity wireline log interpretation, some reservoirs in Nanpu sag have water saturation larger than 50%, however, per oil production testing, those reservoirs have low water production rate. Via FEI QEMSCAN system and FEI scanning electron microscope, the mineral composition, content, distribution and texture of samples from low-resistivity reservoirs in Minghuazhen and Guantao Formation of Nanpu sag have been analyzed. Results show that, the studied samples all have high total clay content, with average volume percentage being 11.62%–15.43%; The main clay minerals of the studied samples are chlorite (average volume percentage 23–35%), illite-smectite mixed layer (average volume percentage 26–31%), and illite (average volume percentage 23–30%). Additional conductivity and absorption of water molecule by these clay minerals are important reasons for the low resistivity wireline response of the studies reservoirs. Pyrite content of the studied samples is 0.08%–3.99% in average volume percentage, and it is highly enriched in several samples, which will increase the electrical conductivity of rock grains of those samples. The back-scattered electron images indicate that the original inter-grain pore with pore diameter being microns contributes the most porosity. However, the clay minerals which broadly, homogeneously and dispersively distribute in samples, as matrix, or part of rock debris, or cement, have effectively enhanced the cation exchange capability of reservoirs, and have created large amount of nano-pores. These nano pores will prominently increase the bound water saturation of reservoirs.

Depositional and diagenetic controls on reservoir heterogeneity and quality of the Bhuban formation, Neogene Surma Group, Srikail Gas Field, Bengal Basin, Bangladesh

This study aims to investigate the controls on reservoir heterogeneity and quality of Miocene Bhuban Formation of the Neogene Surma Group at the Srikail Gas Field, Bengal Basin, Bangladesh. The study integrates wireline log data from two wells with core description as well as petrophysical and petrographic data obtained from 24 core plug samples retrieved from three gas bearing zones. The three zones, namely (from shallower to deeper): D-upper, D-lower, and E-sands, were identified from wireline log interpretation. Based on the extracted cores, the sandstones are classified into three main facies association: 1) coarse grained facies association (CFA) composed of sandstone with parallel lamination, trough, and planar cross bedding; 2) medium grained facies association (MFA) comprises of wavy and flaser bedded sandstone; and 3) fine grained facies association (FFA) consisting of siltstone and shaly sandstone. CFA sandstones, mostly abundant in D-lower and E-sands, were deposited in a high energy distributary channel environment with strong tidal influence while the finer-grained sandstones, mainly present in D-upper sand, were deposited in a low energy distributary channel. The results obtained by integrating core plugs and wireline logs show that best reservoir quality rocks are associated with CFA sandstones which are characterized by GR below 105 API, 15–25% porosity, and 30–100 mD permeability. In contrast, FFA sandstones have lower porosity (<10%) and higher shale content (GR > 125 API). The high energy and strong tidal influence on sandstones of CFA resulted in coarser grain size (and thus larger pores), better sorting and less clay content than the finer-grained, high clay bearing, low energy sediments of FFA. Additionally, petrographic and core plug analyses revealed that mechanical compaction is an important factor that reduces the porosity and permeability with increasing proportions of ductile mineral grains. Other less important diagenetic factors include quartz overgrowth and cement. The findings of this study show that the reservoir quality of the studied field is principally controlled by both depositional environment and mechanical compaction.

Characteristics of collapsed subsurface paleokarst systems and controlling factors of subsurface paleokarst development in the Lianglitage Formation, Halahatang oilfield, Tarim Basin, NW China

The deeply buried Ordovician Lianglitage Formation (>6500 m) in the Halahatang area, Tarim Basin, is characterized by a paleokarst topography and subsurface, collapsed paleokarstsystems. Based on core and thin-section observation and wireline-log interpretation, this study analyzed basic features of collapsed karst systems and mapped the pattern of collapsed and original karst systems through root mean square (RMS) amplitude and variance attribute fusion. Employment of production data revealed the general rule of these ultra-deep, buried, collapsed systems as reservoirs for oil and gas. This study showed that epigenic subsurface karst systems in the Lianglitage Formation experienced full collapse, filling, and subsequent strong compaction. Passages of subsurface karst systems have a dendritic pattern These ultra-deep and strongly compacted collapsed systems are not favorable for oil and gas production owing to poor reservoir qualities. Factors controlling original subsurface karst development in this area are extensive subaerial exposure during the Falling-Stage Systems Tract (FSST) and Lowstand Systems Tract (LST) periods following deposition of the Lianglitage Formation, faults and fractures formed before or during karstification, and surface drainage systems on top of the Lianglitage unconformity. This study provides a method to comprehensively characterize the features, distribution and mechanism of the ultra-deep buried epigenic karst reservoirs and clarified their low potential as reservoirs for oil/gas exploration and development. It also helps clarify that the true oil pay reservoirs in this reservoir resulted from hypogene dissolution rather than epigenic karst.

Factor Analysis of Well Logs for Total Organic Carbon Estimation in Unconventional Reservoirs

Several approaches have been applied for the evaluation of formation organic content. For further developments in the interpretation of organic richness, this research proposes a multivariate statistical method for exploring the interdependencies between the well logs and model parameters. A factor analysis-based approach is presented for the quantitative determination of total organic content of shale formations. Uncorrelated factors are extracted from well logging data using Jöreskog’s algorithm, and then the factor logs are correlated with estimated petrophysical properties. Whereas the first factor holds information on the amount of shaliness, the second is identified as an organic factor. The estimation method is applied both to synthetic and real datasets from different reservoir types and geologic basins, i.e., Derecske Trough in East Hungary (tight gas); Kingak formation in North Slope Alaska, United States of America (shale gas); and shale source rock formations in the Norwegian continental shelf. The estimated total organic content logs are verified by core data and/or results from other indirect estimation methods such as interval inversion, artificial neural networks and cluster analysis. The presented statistical method used for the interpretation of wireline logs offers an effective tool for the evaluation of organic matter content in unconventional reservoirs.

Seismic wave attenuation in carbonate rock and its implication to hydrocarbon-bearing reservoir identification, East Java, Indonesia

The heterogeneity of carbonate rock properties triggers propagated seismic wave to get some attenuations. This mechanism allows that attenuation can be applied in hydrocarbon exploration to identify lithology, porosity, fluid content and fracture identification. Unfortunately, to measure the degree of attenuation, the sophisticated tools and advanced processing technology are required. Thus, some methods were formulated to estimate attenuation. This study is aimed to estimate and compare attenuation from wireline log interpretation by using four different methods. The study is also supported by a series of exploration wells penetrating Kujung I Formation in northwestern edge of North East Java Basin, Indonesia. The result shows that only Qs from Zhang et al method is overestimate. P-wave quality factor of Klimentos and Zhang methods and scaled quality factor (SQp and SQs) method are sensitive to identify hydrocarbon. Furthermore, lithofacies also affects estimated rock quality factor. The novelty of study is to estimate and compare the attenuation from different method and review its result and application in hydrocarbon identification, especially for carbonate reservoir in North East Java basin, Indonesia. So that, a new understanding of attenuation characteristic in carbonate reservoir contributes to discriminate pore fluid identification in hydrocarbon exploration.

Innovative Hydrogeophysical Approaches as Aids to Assess Hungarian Groundwater Bodies

The Hungarian water management plan has lately identified 185 groundwater bodies based on the concepts given by the European Water Framework Directive. Achieving and maintaining the good quantitative and chemical status of these groundwater bodies is of primary importance. It is demonstrated how innovative hydrogeophysical methods can be applied successfully to assess the Hungarian or other international groundwater bodies. By applying geoelectric methods, horizontal layering or large uniform rock units can be well characterized by Wenner–Schlumberger array, also enabling accurate depth determination of the shallow groundwater table. Horizontal variations in the rock type or its state can be well described by dipole–dipole array or, even better, by the newly developed quasi-null arrays. Their joint application may be very straightforward to investigate different aquifer types by giving high-resolution resistivity images as input for hydrogeological modeling. In the identification of porous formations, multivariate statistical interpretation of wireline logs using cluster analysis allows reliable lithological separation of potential aquifers. Their clay content is estimated by robust factor analysis, while their hydraulic properties are directly derived from the resistivity log. For a more effective interpretation, a combination of surface and borehole geophysical methods can be recommended for meeting challenges in hydrogeology and groundwater management.

Petrophysical evaluation of lower Cenomanian Bahariya reservoir, Salam oil field, Shushan basin, north Western Desert, Egypt.

Petrophysical evaluation of the lower Bahariya sediments was performed based on comprehensive interpretation of complete wireline logs suite from two wells in Salam oil field, southwest Shushan basin in the north Western Desert, Egypt. Several petrophysical parameters such as shale volume (VSH), total and effective porosities (PHIT, PHIE), water saturation (SW) and hydrocarbon saturation (SH) were deduced and utilized in the petrophysical subdivision of the lower Bahariya sediments. Neutron versus density, matrix volumetric versus matrix grain density and M-N crossplots revealed that quartzose sandstone is the dominant matrix component within the lower Bahariya sediments. Additionally, the litho-saturation crossplots typified the presence of oil-bearing intervals often associated with the quartzose sandstones with minimal contents of silts and clays. Dispersed and laminated clays are detrimental to the reservoir quality by obstructing the pore spaces and thus reducing the hydrocarbon flow storage and flow capacities. The obtained petrophysical results reveal that the lower Bahariya sediments have a good reservoir quality with high effective porosity values exceeding 18% and low water saturation values ~ 35%. The upper part of the lower Bahariya sediments hosts the most promising reservoir intervals which should be considered during future exploration and development of the oil fields in the study area. Petrophysical evaluation of the lower Bahariya sediments was performed based on comprehensive interpretation of complete wireline logs suite from two wells in Salam oil field, southwest Shushan basin in the north Western Desert, Egypt. Several petrophysical parameters such as shale volume (VSH), total and effective porosities (PHIT, PHIE), water saturation (SW) and hydrocarbon saturation (SH) were deduced and utilized in the petrophysical subdivision of the lower Bahariya sediments. Neutron versus density, matrix volumetric versus matrix grain density and M-N crossplots revealed that quartzose sandstone is the dominant matrix component within the lower Bahariya sediments. Additionally, the litho-saturation crossplots typified the presence of oil-bearing intervals often associated with the quartzose sandstones with minimal contents of silts and clays. Dispersed and laminated clays are detrimental to the reservoir quality by obstructing the pore spaces and thus reducing the hydrocarbon flow storage and flow capacities. The obtained petrophysical results reveal that the lower Bahariya sediments have a good reservoir quality with high effective porosity values exceeding 18% and low water saturation values ~ 35%. The upper part of the lower Bahariya sediments hosts the most promising reservoir intervals which should be considered during future exploration and development of the oil fields in the study area.

FischerLab: An Application for Generating Fischer Plots and Dynamic Fischer Plots from Wireline Well-Logs and Stratigraphic Data

Fischer plots are a technique that is used to graph changes in accommodation in cyclic carbonate successions. They typically depict the cumulative departure from the average cycle thickness as a function of the cycle number or stratigraphic depth. Many applications of Fischer plots focus on their construction from exposed cyclic carbonate successions. No published programs allow the direct construction of Fischer plots from digital wireline well-logs or dynamic presentations of Fischer plots. Here, we introduce a program known as FischerLab, which facilitates the generation and analysis of Fischer plots. In addition to accepting interpreted stratigraphic data input, FischerLab facilitates the interpretation of digital wireline logs for the generation of Fischer plots in cycle and depth domains, as well as in a dynamic evolving cycle and relative depth domain from an easy-to-use interface. The dynamic construction facilitates the correlation of specific stratigraphic packages to parts of the accommodation cycle while simultaneously tracking the locus of the mean subsidence vector. We demonstrate the use of FischerLab on data derived from the carbonate succession outcrops of the Al-Athrun Formation, Libya, and the Glen Rose Formation, Central Texas, USA, as well as on wireline well-log data from the Western Great Bahama Bank, the Bahamas.

Incorporation of Sequence Stratigraphy in Gas Reservoir Correlation: A Case Study

The application of sequence stratigraphy to resolve the miscorrelation between different genetic units in reservoir characterization in a gas field of Surma Basin is dealt with. Interpretation of available seismic and wireline logs (gamma ray, resistivity, density and neutron porosity) give the sequence stratigraphic correlation of reservoir sands. The reservoirs geometry, its extent, seal architecture and trapping styles have been revealed better with this correlation. There is juxtaposition of two reservoir sands, namely A1 and A2. A1 is located at older highstand sand, whereas A2 is in the younger lowstand sand. Lithostratigraphically they might be same but sequences stratigraphy reveals that they are different and deposited at different times. Moreover, the concept reveals that lowstand sand has better reservoir quality than any highstand and transgressive sand.&#x0D; Asiat. Soc. Bangladesh, Sci. 45(2): 209-216, December 2019

Assessment of machine-learning techniques in predicting lithofluid facies logs in hydrocarbon wells

Wireline log interpretation is a well-exercised procedure in the oil and gas industry with all its added value from exploration to production stages. It becomes even more important when it is one of only a few available alternatives to compensate for the lack of core samples in a study of lithologic and fluid variations in a well. Yet, as with other purely expert-oriented interpretational techniques, there is always a considerable risk of subjective or technical errors. We have adopted a hybrid approach that links a machine-learning (ML) algorithm to the log interpretation procedure to solve these problems. We have applied this approach to two different hydrocarbon (HC) fields with the aim of predicting the HC-bearing units in the form of lithofluid facies logs at different well locations. The values of these logs are labels of classes that are separated based on their lithologic and fluid content characteristics. After training different MLs on the designed lithofluid facies logs, we chose a bagged-tree algorithm to predict these logs for the target wells due to its superior performance. This algorithm predicted HC units in an accurate interval (above the HC-fluid contact depth), and it showed a very low false discovery rate. The high-accuracy rate, speed of analysis, and its generalization ability, even in data-deficient cases, accentuate why including ML algorithms can improve the understanding of the subsurface at every phase of the exploration and production process. The proposed approach of using ML algorithms, trained and tuned based on the expert’s knowledge of the reservoir, can be modified and applied to future wells in a HC field to significantly minimize the risk of false HC discoveries.

Petrophysical analysis of well logs for reservoir evaluation: a case study of “Kadanwari” gas field, middle Indus basin, Pakistan

Our study focuses on the interpretation of wire-line logs to evaluate the hydrocarbons potential of sandstone reservoir in the Kadanwari gas field, Sindh, Pakistan. We have considered wire-line logs of four drilled wells (K-01, K-03, K-10, and K-11) in the research area and interpreted 13 reservoir zones. Analytical reservoir analysis includes the shale content (Vsh), effective porosity (Oeff), hydrocarbon and water saturation (Shc and Sw), and net pay thickness variations. Hydrocarbon-bearing zone characterized by high resistivity values, porosity high, permeability high, saturation of water low, and less Vsh suggest clean sand. The petrophysical analysis revealed the hydrocarbon potential of lower Goru sandstone packages at different levels (2886–3797 m). The petrophysical parameters of sub-reservoirs were carefully analyzed which are ranked as good quality sand reservoirs with average effective porosities ranging from 0.11–0.44%, average water saturation ranging from 0.18–0.45%, hydrocarbon saturation averaging between 0.59–0.86%, and permeability ranging from 10.539 to 477.76 m Darcy. Water saturation for heterogeneous shaly sand reservoirs was successfully tested by Indonesian model which suggests that Sw in each well is fewer than 60% therefore over all the region bearing good quality of hydrocarbon potential of the targeted formation and selected zones. The vertical and horizontal variations of reservoir parameters are studied through constructing the litho-saturation cross-plots and isoparametric maps of the petrophysical parameters, respectively. The isoparametric maps help to visualize the geographical distribution of reservoir configuration in the subsurface. The petrophysical estimates of this study appraise the national conventional fuel treasure of lower Goru formation in Kadanwari gas fields and suggest new prospects to drill more wells on the central portion of the southwestern part of the study area. The neighboring area to the south of Kadanwari-01 is economically viable for hydrocarbon exploration. The northeastern side of the study area is avoided due to the high concentration of water and excessive shale content.

Down the borehole but outside the box: innovative approaches to wireline log data interpretation

Wireline logs record the variation in a number of physical measurements, sometimes 20 or more different properties, with depth down a borehole. They are routinely correlated with, and/or interpreted in terms of, the rock stratigraphic record. Logs are also interpreted with the aim of inferring other useful physical properties not directly measured. In some data-rich exploration industries, such as oil and gas, wireline log interpretation is highly developed. In other industries, such as geothermal and minerals exploration, wireline information is often incomplete and may be inaccurate or inconsistent. The aim of this work is to explore an innovative approach to the analysis of wireline logs. We use an innovative, flexible approach to the identification of ?change points?, which may indicate boundaries between lithologies or significant intraformation structure. The number of boundaries/classes is not fixed in advance, being solved for as part of the modelling process. The approaches are applicable in data-rich environments with relatively well-know stratigraphy where they will add to physics and more conventional statistics-based inference. They may also find particular utility in situations with less than ideal data and diverse stratigraphy as they naturally incorporate ways of handling uncertainty. Unforeseen relationships are allowed to emerge and, hence, inform future predictive analysis.

Reinterpretation of Wire-line Log Data in the Eastern Galilee Basin, Queensland: Stratigraphical and Hydrogeological Implications.

The Bureau of Meteorology (BoM) to meet the role of compiling and delivering Australia’s water information under the conditions set out in the Federal Water Act 2007 developed the Australian Water Resource Information System (AWRIS) and the National Groundwater Information System (NGIS) to support AWRIS. Functionality of the NGIS relied on compiling state and territory groundwater databases. Completeness of the data contained in these databases was critical in facilitating data migration to the NGIS and groundwater bores in the Galilee Basin were identified as a priority target for addressing data gaps. Published wire-line log interpretation information was used to create and map structure surfaces for the Galilee Basin. These structure surfaces were used to create a 3D stratigraphic framework to visualise the basin architecture. Assessment of the 3D stratigraphic framework, structure surfaces and wire-line log interpretations identified numerous inconsistencies with the established basin stratigraphy. This is partially attributed to the large number of interpretation sources, exploration relevance and an incomplete understanding of facies variability. Additional areas of concern that were also identified included inconsistent surface geology mapping and a poor understanding of regional lineaments. To address these inconsistencies systematic reinterpretation of the published wire-line log data was undertaken to validate or reassign inconsistent existing stratigraphic interpretations in the Galilee Basin. The highest percentage of inconsistent interpretations was concentrated in the eastern Galilee Basin and this area was chosen as the priority focus area. Reinterpretation relied on utilising a suite of wire-line log data from multiple data sources that included stratigraphic drill holes, coal seam gas (CSG), oil and gas exploration drill holes and groundwater bores. The availability of gamma wire-line log data was the minimum data requirement. Reinterpretation of the wireline log data has resulted in producing revised stratigraphic formation data for the tops of the Moolayember Formation/Base Eromanga Basin, Rewan Group, Dunda beds, Clematis Group, Bandanna Formation/Betts Creek beds, Colinlea Sandstone and Joe Joe Group. This revision has shifted some of these formation tops vertically by up to 300m in some instances leading to significant modification of some structure contour surfaces and the lateral extents of some formations. The Clematis Group, Dunda beds and Rewan Group have undergone the greatest level of modification. Uncertainty over the internal architecture of the Galilee Basin has significant implications for understanding the hydrogeology of aquifer systems and springs in the basin. Reinterpretation by a single operator has assisted in removing some of this uncertainty and provided a consistent dataset of interpretations.