Forward Stratigraphic Modeling of Kuwait Formation, Linking Facies Architecture to Hydrocarbon Occurrence

The objective of this study is to perform forward stratigraphic modeling on the Kuwait Formation (also known as Kuwait Group) exposed stratigraphic succession along the Jal Az-Zor escarpment to explain the enigmatic occurrence of an elongated NW-SE geobody mapped from subsurface data at northern Kuwait. Outcrop measurements such as; stratigraphic successions, facies distribution, critical facies trends, and paleocurrent analysis have been collected along the 60 km length of the Jal Az-Zor escarpment. Such measurements were combined with thin section lab analysis to reveal the various sedimentary processes such as wave activity, grain size distribution, sediment supply sources, accommodation space, and erosional rates. These measurements were combined with subsurface data such as seismic attributes to reconstruct the paleography of the area and run a forward stratigraphic model simulation. The vertical succession was also utilized to reconstruct the relative sea-level fluctuation through time to develop an accurate model. Forward stratigraphic modeling resulted in building a robust and reliable facies distribution 3D model for the Jal Az-Zor escarpment that demonstrates the complex facies architecture. The model shows the various stacking patterns of several depositional sequences that are observed in the field as well as the subsurface. The enigmatic geobody mapped from seismic as a channel system in previous publications turned out to be a paleoshoreline. This shoreline is composed of high-quality sands as a result of an elevated level of wave activity. Reworking of barrier island sands was also found to be responsible for the enhanced reservoir quality. Consequently, regardless of the subsurface structure, the main driver of successful hydrocarbon accumulation is directly linked to the NW-SE trending paleoshoreline. To the best of the authors’ knowledge, this is the first time forward-stratigraphic modeling is performed along the Jal Az-Zor escarpment in north Kuwait and using such an approach to unravel Kuwait Formation heavy hydrocarbon subsurface occurrences.

Influence of Secondary Alterations on the Structure of the Pore Space of the Upper Permian Carbonate Deposits of the Northern Side Zone of the Caspian Basin

The analysis of the facies distribution of reservoirs within the Moscow-Artinskian sedimentation rim within the Northern part of the Pre-Caspian Basin was carried out. The Teplovsko-Tokarevskaya group of deposits is a chain of carbonate structures stretched in the sub-latitudinal direction. They are consist mainly of bioherm structures, which include tubifytes, foraminifera, crinoidea, ostracods, ostracods, etc. From the lithological point of view, the reservoir rocks are represented by dolomite-limestone differences-from organic limestones to secondary chemogenic dolomites. The influence of facies distribution and secondary dolomitization on the structure of the pore space remains controversial and requires detailed study. The concepts of secondary dolomitization were analyzed and one of the concepts of the formation of secondary dolomites and anhydrites was used to justify the facies distribution: Zones of secondary transformation (dolomitization) form a sweet spots zone in the Artinskian carbonate horizon when high-salinity (Mg2+) waters from the Filippovsky horizon carbonates are infiltrates to Artinskian carbonate. As a result of the discharge of elision waters during digenetic dehydration of gypsum. After the anhydride overlaying of the Artinskian carbonate structure, several regressive-transgressive cycles occurred, which formed a sequence of consistent dolomite-limestone and gypsum layers in the Filippovskian time. During the diagenesis water contained in the gypsum was dehydrated into the permeable zones in carbonates of the Filippovsky horizon, followed by unloading in the region of the Artinskian horizon. Evaporite sedimentation of chemogenic carbonates and gypsum created a condition for the subsequent infiltration of sulphate and magnesium waters in the direction dip formation angle. The source of magnesium is the water remaining after the precipitation of gypsum and carbonates in the Filippovskian time.

Case Study: An Approach for Hydraulic Fracturing Minifrac G-Function Analysis in Relation to Facies Distribution in Multilayered Clastic Reservoirs

Summary An industry-accepted standard for minifrac analysis for evaluating and improving design of hydraulic fracturing treatments originated from the original Nolte analysis (Nolte 1979) of pressure decline, followed by the introduction of Castillo G-function in a Cartesian plot (Castillo 1987). The latter provides a graphical method for the identification of fracture closure pressures and stresses with subsequent derivation of other parameters such as fluid efficiency and fracture geometry. With the introduction of a more advanced consideration of the G-function interpretation for various reservoir conditions (Barree et al. 2007), subdividing the interpretation into calculations based on flow regimes and leakoff modes, this approach has become even more sophisticated. Particularly, interesting flow regimes and leakoff modes during fracture closure include the fracture height recession mode. This mode tends to result in rapid screenout and difficulty in placing high proppant concentrations. Regarding interpretation, the G-function derivative curve for this mode can have more than one plateau, an outcome that is possibly indicative of features that have not been widely considered to date or on which little to no data have been published. This paper presents a case study as an example of such height recession mode, along with a subsequent G-function interpretation and analysis and with consideration of the vertical facies distribution along the wellbore. Considerable attention is paid to the G-function derivative plateau analysis. Three distinctive wells, namely X-1,X-2, and X-3, are discussed. Using this technique can lead to an improved fracture calibration, optimized fracture design, and adoption of a successful completion strategy; additionally, the confirmation of 1D facies distribution can provide new insights into the fracture closure period.

Significance of The Sedimentology and Stratigraphy for Identification of Low Contras Low Resistivity zones in a Clastic Outcrop of The Upper Talang Akar Formation, Musi Banyuasin, Indonesia

The Talang Akar Formation is one of the hydrocarbon-producing reservoirs of the South Sumatra Basin. This basin is filled from two different sources in the Eastern part and Western part paleo-high. The bottom Talang Akar consists of coarse-grained sandstone, and the upper part constrains intercalation of sandstone and shale, known as low resistivity low contrast zone (LRLC). The Talang Akar Formation from Air Batu and Sukomoro confers an excellent probability to observe and define LRLC zones over systematic approaches. This paper will provide an analogue of the LRLC reservoir zone by analyzing the relation between facies distribution and reservoir properties, including detailed shale structure. Facies distribution was obtained from the outcrop stratigraphic profile. The reservoir properties are identified by the Thomas Stieber plot and the petrographic section. Seven facies of Talang Akar Formation had been identified, which are: 1) planar cross-bedded sandstone (PCBS), 2) trough cross-bedded sandstone (TCBSS), 3) laminated sandstone (LSS), 4) heterolytic sandstone (HSS), 5) clay-rich sandstone (CSS), 6) mudstone (MS), 7) scour conglomeratic sandstone (SCSS). There are several types of shale distribution: structural shale, dispersed shale, and laminar shale. The laminar and dispersed shale consists of most of the reservoir and fills the pore. The clay structure deduces the disparity in the facies-porosity correlation. The finding of this study revealed that the LRLC zones are caused by lamination structures, thin intercalation layers, heterolytic and clay minerals.

Tectonic–sedimentary interplay of a confined deepwater system in a foreland basin setting: the Pennsylvanian lower Atoka Formation, Ouachita Mountains, U.S.A.

ABSTRACT Submarine fans deposited in structurally complex settings record important information on basin evolution and tectonic–sedimentary relationships but are often poorly preserved in outcrops due to syndepositional and post depositional deformation. This study aims to understand the influence of tectonics on the deposition of the synorogenic Pennsylvanian lower Atoka submarine fan system deposited in a structurally complex foreland basin during the Ouachita orogeny. This study is a synthesis of new outcrop stratigraphic data as well as published stratigraphic and structural data. The lower Atoka crops out in the Ouachita Mountains and the southern Arkoma Basin and is divided into three structural–depositional zones: the foredeep, the wedge top, and the continental foreland. The mean paleoflow is axial, and each zone exhibits unique patterns in facies distribution. The foredeep consists of two fan systems, a large westward-prograding fan that exhibits significant longitudinal and lateral facies changes, and a small eastward-prograding fan on the western part. The wedge top consists of a westward-prograding fan that exhibits subtle longitudinal facies change. The continental foreland consists of small slope fan systems along the northern and western margins. By comparing to basin morphology and structural styles, we interpret the facies distribution patterns in the three zones as the result of different combinations of lateral structural confinement, axial and lateral sediment supply, and paleogeography. This study provides an improved and comprehensive understanding of the lower Atoka deepwater system and has implications for deciphering the tectonic–sedimentary relationships in laterally confined submarine fan systems.