Reservoir Facies Research Articles

Application of attribute-based inversion and spectral decomposition with red–green–blue colour blending for visualization of geological features: a case study from the Kalol Field, Cambay Basin, India

The Kalol Field in the Cambay Basin of India was discovered in 1961 and has been producing through more than 608 wells from Kalol reservoirs but the cumulative production up until 2008 was only 95.19 MMbbl. Reasons for low recovery have been ascribed to poor reservoir facies and limited reservoir thicknesses. In the Kalol Field, several thin clastic reservoirs are sandwiched within the main reservoir and exhibit lateral variations in lithology. Attribute-based inversion (ABI) is effective at delineating potentially prospective areas and reveals the existence of a good reservoir facies cluster in the south, SE and NW corners of our study area, near the Kalol Field. However, this method cannot decipher the depositional setting or the finer details of facies elements. To obtain a smooth and fine-tuned facies model, geostatistical modelling is adopted taking the ABI output (seismic-facies model) as the initial model. The advantage of geostatistical modelling is that it always honours the input data and respects the positional variograms of the geology. Adding spectral decomposition with red–green–blue (SD-RGB) colour blending reveals the existence of a meandering river in the study area. This river is interpreted to have deposited crevasse splays and channel facies along the river banks. These two facies are the main producing contributors to a well that has maintained a higher production than any other well in this field. This facies-based approach is also effective in determining the reservoir geometry and quality consistent with the interpretation of the depositional environment. In ABI, 3D attribute volumes of petrophysical properties are calculated using a genetic algorithm inversion and artificial neural network using a non-linear correlation between seismic and log properties. The calculated 3D attribute volumes of petrophysical properties are subsequently utilized for seismic facies classification. In contrast to ABI, SD-RGB colour blending has been solely utilized for co-visualization of different band-limited amplitude volumes from spectral decomposition. Conventional seismic inversion has now been replaced by an integrated approach combining ABI, geostatistical modelling and SD-RGB colour blending in an effort to delineate the remaining potential of the field, and to improve the geological success and ultimate recovery.

An interdisciplinary approach to reservoir characterisation; an example from the early to middle Eocene Kaimiro Formation, Taranaki Basin, New Zealand

Abstract The Kaimiro Formation is an early to middle Eocene, NE-SW trending reservoir fairway in Taranaki Basin, and comprises a range of coastal plain through to shallow marine facies. A time of regional transgression is observed across the Paleocene–Eocene transition, which is linked to a general global warming trend and to regional thermal relaxation-related subsidence in New Zealand. The earliest Eocene transgressive deposits pass upwards into a series of cyclically stacked packages, interpreted as 3rd and 4th order sequences. Maximum regression occurred within the early Eocene and was followed by punctuated retrogradational stacking patterns associated with shoreline retreat and subsequent regional transgression in the middle Eocene. The Kaimiro Formation is considered a good reservoir target along most of the reservoir fairway, which can largely be attributed to a consistently quartz-rich, lithic-poor composition and reasonably coarse sand grain size. Correlations demonstrate that within the early Eocene the main reservoir facies are channel-fill sandstones overlying candidate sequence boundaries in paleoenvironmentally landward (proximal) settings, and upper shoreface/shoreline sandstones in relatively basinward (distal) settings. Middle Eocene reservoir facies are not represented in distal wells due to overall transgression at this time, yet they form a significant target in more proximal well locations, particularly on the Taranaki Peninsula. Depositional facies is one of the principal controls on sandstone reservoir quality. However, while reservoir facies have been proven along the length of the reservoir fairway, it is evident that diagenesis has significantly impacted sandstone quality. Relatively poor reservoir properties are predicted for deeply buried parts of the basin (maximum burial >4.5 km) due to severe compaction and relatively abundant authigenic quartz and illite. In contrast, good reservoir properties are locally represented in reservoir facies where present-day burial depths are These results illustrate how an interdisciplinary approach to regional reservoir characterisation are used to help reduce risk during prospect evaluation. Assessment of both reservoir distribution and quality is necessary and can be undertaken through integrated studies of facies, sequence stratigraphy, burial modelling and petrography.

Detection of a deep-water channel in 3D seismic data using the sweetness attribute and seismic geomorphology: a case study from the Taranaki Basin, New Zealand

ABSTRACTIn recent years, the three-dimensional seismic method has become an essential tool for the interpretation of subsurface stratigraphy and depositional systems. Seismic stratigraphy, in conjunction with seismic geomorphology, has elevated the degree to which seismic data can facilitate geological interpretation, especially in deep-water environments. Techniques such as time slicing and interval attribute analysis can enhance geomorphological interpretations and, when integrated with stratigraphic analyses, can yield insights regarding the distribution of seal and reservoir facies. Sweetness is a seismic attribute that can be very useful for channel detection in deep-water clastic settings, especially when used in conjunction with coherency in plan view. In this article, we present an example of a deep-water channel complex from a three-dimensional seismic volume that is derived using co-rendered sweetness and semblance attributes. The advantages of and workflow followed for the co-rendered attributes are discussed. The application of this technique to a dataset in the offshore Taranaki Basin, New Zealand, has led to the observation of four channel elements: (1) point-bars, (2) the migration of channel meander loops, (3) channel erosion and cutting, and (4) avulsion. This technique enables the detailed visualisation of complex depositional elements, and could be used to predict sands in the channel systems, which is of vital importance for evaluating the distribution of deep-water sandstone reservoirs. The technique is applied to the study area in an effort to illustrate the variety of interpretation techniques available to the geoscientist.

A Natural Gamma Spectrometry Approach to Derive Clay Mineral Composition and Depositional Environment of a Reservoir Facies in Ramnad Sub-basin, Cauvery Basin, Southern India

ABSTRACT The Ramnad sub-basin is one of the most explored for hydrocarbons in Cauvery basin. A number of exploratory wells have been drilled to delineate hydrocarbon bearing horizons. Nannilam Formation of Santonian – Campanian age hosts considerable thickness of reservoir facies. The reservoir facies is mainly clastics such as sandstone and siltstone with lot of clay content. In addition to normal logs, the NGS (Natural Gamma Ray Spectrometry) logs are widely employed to estimate sediment composition and broad depositional environment of reservoir facies. The present study employs and analyses NGS logs of four well sections from Kanjirangudi area of Ramnad sub-basin to determine the clay mineral composition and depositional environment of Nannilam Formation. Thorium (Th), potassium (K) and uranium (U) concentrations and their interrelationships reveal that montmorillonite, illite and kaolinite are the dominant clay minerals. The clay mineral composition suggests that the sediments of the Nannilam Formation were derived from a provenance of acid igneous rocks during warm, humid and tropical conditions. Also, the ratios of Th/K indicate a deep open marine condition under which the sediments of the Nannilam Formation were deposited. These results would aid a better understanding and characterization of reservoir facies in the sub-basin.

Lithofacies paleogeography and sedimentary model of Sinian Dengying Fm in the Sichuan Basin

Abstract For predicting the distribution of favorable reservoir facies belts of the super-large ancient Anyue carbonate gas field in the Sichuan Basin, through an analysis of structure and lithofacies paleogeography, the lithofacies paleogeography and sedimentary model of the Sinian Dengying Fm was reconstructed based on the field outcrop, drilling and seismic data. As a result, achievements are made in four aspects. First, the basin and its periphery resided in an extensional tectonic setting in the Sinian. Intense extension led to the formation of the Deyang–Anyue intra-platform rift. The Sichuan Basin was divided into the palaeo-geographic pattern of “two uplifts and four sags”. The “two uplifts” evolved into the platform, and the “four sags” evolved into the slope-basin environment. Second, in the depositional stage of the Deng 2 Member, some favorable reservoir belts developed, such as bioherm-shoal at the continental margin, bioherm-shoal at the rift margin, and bioherm-shoal in the platform. The bioherm-shoal at rift margin developed along both sides of the Deyang–Anyue rift, in a U-shape, with a width of about 5–40 km and a length of about 500 km. It connected with the platform margin belt at the continental margin to the west in the Shifang area, and to the north near Guangyuan area. Third, in the depositional stage of the Deng 4 Member, when the lithofacies paleogeographic features in the Deng 2 Member remained, the platform margin belt at the rift margin evolved into two parts in the east and the west as a result of the continuous southward extensional faulting of the Deyang–Anyue rift until it finally crossed the basin from north to south. The eastern platform margin belt was located in the Guangyuan–Yanting–Anyue–Luzhou area, showing NS distribution with a length of about 450 km and a width of about 4–50 km. The western platform margin belt mainly developed in the Dujiangyan–Chengdu–Weiyuan–Yibin–Mabian area, showing an eastward arc distribution with a length of about 300 km and a width of 4–30 km. And fourth, the sedimentary model of rimmed platform with double platform margins in the Dengying Fm was established, providing a guidance for predicting the distribution of favorable reservoir facies belts.

Seismic prediction on the favorable efficient development areas of the Longwangmiao Fm gas reservoir in the Gaoshiti–Moxi area, Sichuan Basin

Abstract The Lower Cambrian Longwangmiao Fm gas reservoir in the Gaoshiti–Moxi area, the Sichuan Basin, is a super giant monoblock marine carbonate gas reservoir with its single size being the largest in China. The key to the realization of high and stable production gas wells in this gas reservoir is to identify accurately high-permeability zones where there are dissolved pores or dissolved pores are superimposed with fractures. However, high quality dolomite reservoirs are characterized by large burial depth and strong heterogeneity, so reservoir prediction is of difficult. In this paper, related seismic researches were carried out and supporting technologies were developed as follows. First, a geologic model was built after an analysis of the existing data and forward modeling was carried out to establish a reservoir seismic response model. Second, by virtue of well-oriented amplitude processing technology, spherical diffusion compensation factor was obtained based on VSP well logging data and the true amplitude of seismic data was recovered. Third, the resolution of deep seismic data was improved by using the well-oriented high-resolution frequency-expanding technology and prestack time migration data of high quality was acquired. And fourth, multiple shoal facies reservoirs were traced by using the global automatic seismic interpretation technology which is based on stratigraphic model, multiple reservoirs which are laterally continuous and vertically superimposed could be predicted, and the areal distribution of high quality reservoirs could be described accurately and efficiently. By virtue of the supporting technologies, drilling trajectory is positioned accurately, and the deployed development wells all have high yield. These technologies also promote the construction of a modern supergiant gas field of tens of billions of cubic meters.

The mid-Cretaceous Natih Formation in Oman: A model for carbonate platforms and organic-rich intrashelf basins

The Natih Formation in Oman is an exceptionally well–exposed and studied example of a large (>1000 km [621 mi]) epeiric, shallow marine, tropical carbonate platform system with adjacent organic-rich intrashelf basins. It serves as an outcrop analog for many of the mid-Cretaceous giant oil reservoirs as well as for unconventional reservoirs in the Mesozoic of the Arabian plate. A key feature of the Natih Formation is its strict hierarchical stratigraphic organization at multiple orders of depositional sequences (third to fifth), which was first demonstrated in outcrop and subsequently adopted in the seismic and log data sets of the nearby subsurface. It has provided a high-resolution time framework for the robust sequence stratigraphic model that has been developed for an area of 6000 km2 (2317 mi2). Deposited in a calm tectonic setting, the Natih Formation provides an excellent example to demonstrate the principles of carbonate systems’ response to eustatic sea level change and some fundamental differences with siliciclastic systems. Key aspects that are addressed include the influence of the rate of sea level rise on the transition from ramp to platform, the creation of organic-rich intrashelf basins through differential accumulation rates, changing facies models within third-order sequences, and the importance of different platform top channel types. The economic relevance of this case study is the improved prediction of reservoir, seal, and source rock facies distribution and the associated early diagenetic overprint, insights that have been applied in the reservoir modeling of nearby oil fields as well as in exploration-scale studies.

Reservoir quality variations within a conglomeratic fan-delta system in the Mahu sag, northwestern Junggar Basin: Characteristics and controlling factors

The conglomeratic reservoir in the Mahu depression, northwestern margin of the Junggar basin, Northwestern China has become an important exploration target. In this study, we use well and core data to investigate the characteristics and controlling factors of conglomeratic fan-delta reservoirs. The reservoir studied here developed in a retreating fan-delta complex that is dominated by conglomerate lithofacies and conglomeratic sandstone lithofacies. A petrological analysis shows that the reservoir exhibits poor compositional maturity and textural maturity. A physical property analysis shows that the reservoir exhibits extremely low porosity and extremely low permeability, as well as strong heterogeneity in the vertical and planar views. The depositional environment and compaction result in extremely low porosity and extremely low permeability in the reservoir. About 66% porosity was destroyed by the compaction. Fan-delta evolution and provenance control the macroscopic variations in reservoir quality. Muddy matrix content, grain size and dissolution control the microscopic variations in reservoir quality. About 52.5% porosity was induced by the dissolution. This reservoir study can be compared to fan-deltas that developed in marine-connected rift basins during early stages of extension and to nearshore subaqueous fans in East China. Additionally, the results of this study may provide a reference for such systems and provide a subsurface case for similar fan-delta outcrop studies and facies reservoir modelling.

Reservoir properties prediction using extended elastic impedance: the case of Nianga field of West African Congo basin

Simultaneous seismic inversion and extended elastic impedance (EEI) were applied to obtain quantitative estimates of porosity, water saturation, and shale volume over Nianga field of Congo basin, West Africa. The optimum angle at which EEI log and the target petrophysical parameter give the maximum correlation was meticulously analyzed by additionally incorporating the concept of relative rock physics. Prestack seismic data were simultaneously inverted into Vp, acoustic, and gradient impedances. The last two broadband inverted volumes were projected to Chi angles corresponding to the target petrophysical parameters, and three broadband EEI volumes were obtained. At well control points, the linear trends based on specific lithology between EEI and petrophysical parameters were then used to transform EEI volumes into quantitative porosity, water saturation, and shale volume cubes. In order to obtain the reservoir facies distribution, another concept of minimum energy angle was used to generate the background EEI cube, thereby enabling the mapping of reservoir facies. From quantitative porosity, water saturation, shale content, and background EEI cubes, favorable zones have been pinpointed which may suggest possible drilling locations for future development of the field.

Geologic-carbon-sequestration potential of the Ordovician St. Peter Sandstone, Michigan and Illinois Basins, United States

Cambrian–Ordovician strata of the midwestern United States are considered a promising reservoir for geologic storage of carbon dioxide. To assess the potential of the Ordovician St. Peter Sandstone, storage-resource estimates were generated using a hierarchical approach to estimating prospective storage resources. The method employs a series of increasingly sophisticated analyses to better facilitate an understanding of the uncertainty in the estimates. Results demonstrate how uncertainty of storage-resource estimates varies as a function of data availability and quality as well as the underlying assumptions used in the application of specific storage efficiency factors. In the simplest analysis, storage-resource estimates were calculated from updated regional-scale mapping of the gross thickness of the formation and by applying a single best estimate of the mean porosity for the entire formation. This analysis follows the technique prescribed by the US Department of Energy and yields storage-resource estimates ranging from 3.3 to 35.1 billion t CO2 in the Michigan Basin and 1.0 to 11.0 billion t CO2 in the Illinois Basin at the 10% and 90% probability levels. The second analysis incorporated generalized models of the diagenetic history of the formation throughout the two basins by implementing depth-dependent functions of porosity that lead to more realistic portrayals of spatially variable results. Similar resource estimates were calculated for the Michigan Basin, but reduced estimates (43%) were found for the Illinois Basin. The third analysis explicitly accounted for the local-scale spatial variability in reservoir quality using net-porosity calculations, resulting in a significant increase in the low-range resource estimate for the Michigan Basin and dramatic increases for Illinois Basin resource estimates (factor of 3 to 11 increases). A fourth analysis was conducted for the Michigan Basin that used advanced reservoir characterization to define reservoir properties for multiple reservoir facies and yielded resource estimates significantly larger than the third analysis and a larger range of uncertainty. This study highlights how different factors impact the expected uncertainty in storage-resource estimates, and analysis suggests that estimates from the first two approaches provide excessively conservative results, whereas the second two approaches tend to overestimate the resource.

3D Close-the-Loop Method Based on Probabilistic Seismic Inversion

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 18913, “3D Close the Loop Using Probabilistic Seismic Inversion for a Gas Field in the Carnarvon Basin, Australia,” by Shilpi Srivastava, Jeroen Goudswaard, Sito Busman, and Justin Ugbo, Shell, prepared for the 2016 International Petroleum Technology Conference, Bangkok, Thailand, 14–16 November. The paper has not been peer reviewed. Copyright 2016 International Petroleum Technology Conference. Reproduced by permission. The paper discusses an approach for predicting the lateral variation of net to gross (NTG) by use of 3D probabilistic seismic inversion. The goal is to define and understand the distribution of sands and shales on the basis of seismic reflection data. The modeling and inversion are supported by the good quality of seismic data. This study underpins the benefits of seismically constrained reservoir modeling. The use of probabilistic inversion to map geological features is a new insight in the applicability of this methodology. Introduction The study field is located in the Carnarvon Basin offshore western Australia. The field was appraised with one well, which has added incremental volumes to existing nearby discoveries. Seismically constrained reservoir-model building creates models that are constrained by, and matched to, geological concepts and seismic amplitudes and travel times. The complete paper shows an approach using 3D probabilistic seismic inversion to predict the lateral variation in NTG over a proven discovery. This, in turn, can be used to update the static-model properties, improving on the first-pass static-model build. Additionally, the inversion will aid in the understanding of some poorly understood seismic expressions, especially in the south of the field. In this area, the authors noticed dim amplitudes on the amplitude maps extracted from the seismic data, where the static model predicts the presence of the reservoir. Field The field is located in the Carnarvon Basin. The discovery was appraised by one well, which penetrated a thin sand layer of interdistributary bay reservoir facies (referred to as Sand 1) and a thicker distributary channel facies (referred to as Sand 2). The overburden comprises basinal shales and marls. The main steps in the 3D close-the-loop work flow are The rock-property-trend models are derived using the available vertical wells in or near the field. A “rock model” is a set of equations that honors well data and links the petrophysical properties such as NTG and porosity with rock acoustic properties. A qualitative 3D check-the-loop (CTL) step is carried out. This involves the initial fit of the static model with the seismic data by forward modeling the synthetic seismic computed from the initial static model before inversion. The quality-control step that follows aims to detect mismatches between seismic and synthetic data. Finally, constrain the reservoir model by use of the seismic data by carrying out 3D probabilistic inversion of the key uncertain rock property.

The stratigraphic architecture and depositional environments of non-marine carbonates from barremian-aptian pre-salt strata of the Brazilian continental margin

The stratigraphic architecture and depositional environments of non-marine carbonates from barremian-aptian pre-salt strata of the Brazilian continental margin

Paleoenvironment of deposition of Miocene succession in well BK-10 of Bengal Basin using electrofacies and lithofacies modeling approaches

Integrating well log and core samples data were applied to interpret paleoenvironment of deposition of Miocene succession for understanding of reservoir facies model from a well Bakhrabad (BK)-10 of Bengal Basin. Miocene succession was subdivided into two depositional sequences/models which contain 9 para sequence sets and 35 para sequences. Detailed examination of well log data, based on considering GR (gamma ray) log shapes, size, lithologic variations permit a subdivision into five electrofacies models, e.g., bell, funnel, cylindrical, egg/bow and linear shape models. The succession consists of alternating shales, shaly sand, silts and sandstones, with minor mudstones. The study revealed eight distinct lithofacies models namely, shale dominated facies, heterolithic sandstone facies, cross bedding facies, parallel laminated shale with alternate sand/silt facies, ripple-lamination facies, bioturbation facies, wavy bedded facies and laminated shale facies. The depositional models for the Miocene sediments encountered in the studied well BK-10 inferred to be that of delta-front setting and fluvio-deltaic to shallow marine environments. Based on lithofacies and electrofacies models associations, Miocene succession interpreted as a coarsening upward deltaic progradation; although more repetitive marine transgression and regression sedimentary processes might have an impact on the architecture of reservoir facies model.

Electrofacies vs. lithofacies sandstone reservoir characterization Campanian sequence, Arshad gas/oil field, Central Sirt Basin, Libya

Abstract The present study focuses on the vertically stacked sandstones of the Arshad Sandstone in Arshad gas/oil field, Central Sirt Basin, Libya, and is based on the conventional cores analysis and wireline log interpretation. Six lithofacies types (F1 to F6) were identified based on the lithology , sedimentary structures and biogenic features, and are supported by wireline log calibration. From which four types (F1-F4) represent the main Campanian sandstone reservoirs in the Arshad gas/oil field. Lithofacies F5 is the basal conglomerates at the lower part of the Arshad sandstones. The Paleozoic Gargaf Formation is represented by lithofacies F6 which is the source provenance for the above lithofacies types. Arshad sediments are interpreted to be deposited in shallow marginal and nearshore marine environment influenced by waves and storms representing interactive shelf to fluvio-marine conditions. The main seal rocks are the Campanian Sirte shale deposited in a major flooding events during sea level rise . It is contended that the syn-depositional tectonics controlled the distribution of the reservoir facies in time and space. In addition, the post-depositional changes controlled the reservoir quality and performance. Petrophysical interpretation from the porosity log values were confirmed by the conventional core measurements of the different sandstone lithofacies types. Porosity ranges from 5 to 20% and permeability is between 0 and 20 mD. Petrophysical cut-off summary of the lower part of the clastic dominated sequence ( i. e. Arshad Sandstone) calculated from six wells includes net pay sand ranging from 19.5′ to 202.05′, average porosity from 7.7 to 15% and water saturation from 19 to 58%.

Facies and Reservoir Characteristics of the Ngrayong Sandstone in the Rembang Area, Northeast Java (Indonesia)

The Rembang area is a well-known prospective region for oil and gas exploration in Northeast Java, Indonesia. In this study, the reservoir characteristics of the Ngrayong Sandstone were investigated based on outcrops in the Rembang area. Petrological, mineralogical, petrophysical and sedimentological facies analyses were conducted. These sandstones are grain- and matrix-supported, and composed of very fine to medium, sub-angular to poorly-rounded, moderately- to very well-sorted sand grains. These sandstones are mainly composed of quartz, orthoclase, plagioclase, and micas with minor amounts of clay minerals, and therefore are predominantly classified as sub-lithic arenite and sub-felds pathicarenite. Petrographic observations and grain size data indicate that these sandstones are texturally quite mature, based on their good-sorting and the occurrence of minor amounts of matrix clays. Common clays in the samples include illite, smectite, kaolinite, and gibbsite. The porosity of the Ngrayong sandstones ranges from 25.97% to 40.21%, and the permeability ranges from 94.6 to 3385 millidarcies. Thus, these sandstones exhibit well to excellent reservoir qualities. Eight lithofacies were identified from five measured stratigraphic sections, and are dominated by foreshore and tide-dominated shoreface facies. The Ngrayong sequence shows a single transgressive-regressive cycle. Cross-bedded sandstone and massive sandstone are identified as the most promising potential reservoir facies based on their characteristics in outcrops, their lateral and vertical distributions, their sedimentological characteristics and their petrophysical properties.

Sarvak Reservoir Facies Characteristics in One of the South West Field in Iran

Sarvak Formation (Late Albian-Early Turonian) as main reservoir in the field is one of the carbonate units of Bangestan Group in Zagros Basin with average thickness of 640 m. This formation conformably overlays the Kazhdumi Formation while the upper boundary is an erosional unconformity which is covered by Ilam Formation. There is a significant lateral and vertical heterogeneity in the reservoir layers that causes main challenge in reservoir characterization. In this paper, reservoir properties evaluation and construction of depositional model have been done based on lithotype study, sedimentary environment classification, petrophysical interpretations and SeisWorks. Five facies types (lithotypes) in the Sarvak Formation with particular rock properties are identified in 8 wells and 200 thin sections. The main facies association elements and relevant depositional settings have been interpreted by extracted Paleolog, facies and fossil association data which are related to depositional setting variations.

The sedimentary facies characteristics and lithofacies palaeogeography during Middle-Late Cambrian, Sichuan Basin and adjacent area

Abstract Combined with the regional strata filling characteristics of Middle-Upper Cambrian, the present paper conducts a systematic research on sedimentary facies in the basin and its peripheral area by utilizing 164 field outcrops and drilling and coring data. Further, the method of “multi-factor comprehensive synthesis based on single-factor analysis” was employed to investigate the sedimentary facies and palaeogeography of the study area and establish the sedimentary facies model. Stratigraphic reveals that the study area represents the pattern of thin-northwest and thick-southeast by stretching northeast-southwest. Within the present basin, the pattern of “one thin and two thick” predominates, while outside the basin “four thin and three thick” filling feature was found. Sedimentary facies shows that the study area was featured by rimmed carbonate platform. Specifically, carbonate platform, slope and northeastern corner Qinling paleooceanic Basin and southeastern corner Jiangnan Bain was identified from the west to the east. The carbonate platform contains restricted platform, evaporation-restricted platform, semi-restricted platform and the platform margin. Single factor analysis and lithofacies palaeogeographic characteristics manifests that during Middle-Late Cambrian, the western Old land evolved into peneplain stage, and that the eastern and southwestern sub-sags remained connected to the open-sea to some extent. At the time, the shllow seawater circulation was relatively restricted, while the ancient seabed tended to be flat and evaporation characteristics significantly diminished. Secondary sea-level fluctuation intensively influenced the development of scaled grain beach. It is suggested that tide marginal beach, intraplatform shoal subfacies zone, along with Shiqian-SangZhi in southeast and Zhenba-Xinshan in northeast platform-margin beach subfacies zone to be preferable targets for the favorable reservoir facies zone and potential oil and gas reservoir area.

Evaluating distribution pattern of petrophysical properties and their monitoring under a hybrid intelligent based method in southwest oil field of Iran

This study deals with reservoir characterization based on well log data using an unsupervised self-organizing map (SOM) and supervised neural network algorithms with the aim of clustering log responses into reservoir facies of an oil field located in southwest of Iran. In order to promote and justify the quality control and quantify spatial relationships for petrophysical properties, some of neural network-based approaches were introduced such as the SOMs as the intelligent clustering method compared with other hybrid methods, principal component analysis networks (PCANs) and multilayer perceptron (MLP) and statistical clustering (CA) methods. The results obtained from all the abovementioned methods are compared to each other, and the best option is selected based on accuracy and capabilities of clustering and estimation of the petrophysical data, concluding that for predicting any characteristic of the reservoirs, the appropriate network should be chosen and a unique network cannot be convenient for all of them. Accordingly, the SOM clustering technique was employed to classify the reservoir rocks. Based on the SOM visualization, the reservoir rocks were classified into six facies associated with specific petrophysical properties; among them, F6 expressed the best reservoir quality which is characterized by the low amount of density, highest DT, high amount of neutron porosity (NPHI), and lowest GR response. Ultimately, the performance of all the methods was compared to estimate the porosity and permeability within each facies. The results revealed the preference and reliability of PCAN in predicting porosity and confirmed the capability of MLP in permeability prediction. This study also indicates that neuro-prediction of formation properties using well log data is a feasible methodology for optimization of exploration programs and reduction of expenditure by delineating potentially oil-bearing strata with higher accuracy and lower expenses. The resulting neural net-based model can be used as a powerful and distributive system to reduce the high impact of risk in similar fields.

Characterization of a reservoir ooid shoal complex and Artificial Neural Networks application in lithofacies prediction: Mississippian St. Louis formation, Lakin fields, western Kansas

Abstract Residing in the Hugoton embayment of western Kansas, the Lakin field has produced over 1.8 million bbl of oil from reservoir quality zones within the St. Louis Limestone (Mississippian, Meramecian) oolitic deposits. This study focuses on improving the understanding of the orientation, geometry, and spatial distribution of ooid shoal complexes in Kearny County, Kansas. To this end, the interpretation of petrophysical log data integrated with a facies analysis conducted on 400 ft (122 m) of core from three separate intervals provided the basis, in this study, for understanding the vertical stacking patterns and how facies transitions relate to reservoir quality zones within the ooid shoal complexes. A supervised Artificial Neural Network (ANN) has been trained and validated, based on input-layer of geophysical well-logs and an output-layer of core-lithofacies, for lithofacies prediction where core samples were not available. The porous ooid grainstone is the principal reservoir facies, with an average log-derived porosity measurement of eighteen percent. Ooid shoal complexes are present in St. Louis Zone B and C, with thicknesses reaching up to 10 ft (3 m) and 24 ft (7 m) respectively. These complexes are NW-SE trending and laterally extend up to 16 mi (26 km), with economically viable patches covering up to 8 mile (13 km), and record roughly 2 mile (3 km) in width. The apex of the shoal contains the highest porosity values, with significant porosity reduction towards the shoal margins due to the increased cementation. This study provides information on the characteristics of oolitic deposits for the purpose of understanding controls on reservoir heterogeneity to aid in finding additional hydrocarbon reserves in the St. Louis Limestone in western Kansas.

Fuzzy classifier fusion: an application to reservoir facies identification

An application of classifier fusion technique is presented to improve the performance of automated reservoir facies identification system. The algorithm presented in this study uses three well-known classifiers, namely Bayesian, k-nearest neighbor (kNN), and support vector machine (SVM) to automatically identify four defined facies of Asmari Formation from log-derived amplitude versus offset (AVO) attributes. Fuzzy Sugeno integral (FSI) method is then employed to combine the outputs of three investigated classifiers and increase the consistency of reservoir facies identification process. The experimental results obtained from applying the presented algorithm on data related to three wells drilled in Asmari Formation provide evidence of the effectiveness of the proposed algorithm regarding true positive (TP), false positive (FP), and classification accuracy criteria.