Prediction of Reservoir Quality & Deliverability of the Tight Barik Formation in Khazzan Field, Oman

The giant Khazzan gas field, located in onshore Oman, has been under development since 2013 and in production since 2017. The field is currently producing 1 billion cubic feet of gas per day from the Cambro-Ordovician Barik Formation. The 80-metre-thick paralic reservoir is 4.5 kilometers deep and has undergone complex stages of diagenesis, hydrocarbon charge and structural regime changes. Reservoir quality (RQ) is typically classed as tight (average porosity 6 porosity unit, average permeability 1 Milidarcy) but locally exceeds expectations given the burial history reaching up to 12 pu and 100 Milidarcy. This RQ variability and complexity makes reservoir deliverability (RD) a key uncertainty impacting the field development scheme and ultimately the projected economics. This study aims to create and test hypotheses of RQ and RD controls to reduce uncertainty in production and increase reservoir development efficiency. In order to better understand the key controls on reservoir quality, an extensive set of core, petrophysical log analysis and production data were integrated with field-wide seismic and outcrop data to update the Barik stratigraphic, structural and depositional frameworks. Extensive analytical techniques, including reservoir quality modelling, petrographic analysis, X-ray diffraction, mercury injection capillary pressure and minipermeameter data were also integrated. Quartz cementation and compaction are the principal degrading controls on reservoir quality. The controls on quartz cementation are complex and variably inter-related, although in general it is ductile content, proximity to mudstone and feldspar content that are the best predictors of porosity and permeability when convolved. Minipermeameter data confirms that distance to mudstone, or sandstone thickness, is an important control on reservoir quality. Using normalized gamma ray log data, total and mean individual sandstone thickness were calculated for every Barik well in Khazzan and compared to well dynamic behavior which demonstrated a positive correlation. Areas with high mean individual sandstone thickness and total sandstone thickness frequently equate with relatively high IP30s (average well production at 1100 psi well head pressure for 30 days). In contrast, areas with high total sandstone thickness, but low mean individual sandstone thickness may only have moderate IP30s as those sandstones may be more quartz cemented. Reservoir deliverability risk maps based on total and mean individual sandstone thickness and IP30 were constructed. These maps give insight into regions of poor and good gas deliverability and have identified areas that may be untested or undeveloped that may have potential upside. The resultant reservoir deliverability understanding of the Barik formation is consistent with depositional environment, diagenetic understanding and well performance. It is a good example of integrating diverse static and dynamic data to improve reservoir understanding and has direct business impact.

Late Miocene paleogeography and flora of north-western Wairarapa, New Zealand

<p>The Late Miocene flora and paleogeography of north-western Wairarapa were determined by examining and sampling the Upper Miocene marine and non-marine deposits of the Mangaoranga Formation. This formation unconformably overlies Mesozoic greywacke basement in areas of north-west Wairarapa and contains the oldest sediments preserved immediately overlying basement in this area. Little work has been carried out previously to fully understand the depositional history of the formation or the surrounding vegetation cover. Thus, the present study is intended to improve interpretations of the Late Miocene paleogeography and flora of north-western Wairarapa. The strata of the Mangaoranga Formation were examined at three locations in north-western Wairarapa: at Mangaoranga Stream (Eketahuna), Central Mangaone Road (Eketahuna) and Mauriceville. For paleogeographic reconstructions, the strata were described at Mangaoranga Stream and subsequently correlated to strata at the Mauriceville and Central Mangaone Road sites. The formation was sampled several times at each site for palynological analysis. Additionally, samples available for pollen analysis from the Mt Bruce and Alfredton areas were also examined. The results of these analyses, in conjunction with mummified leaves, aided reconstructions of the Late Miocene vegetation cover. Fission-track analysis on apatite grains from Torlesse basement immediately below the formation was also undertaken, providing evidence for the cooling (and hence exhumation) and subsequent burial history of the basement strata. The results of the apatite fission-track analysis suggest that exhumation of the basement strata above the apatite closure temperature (110ºC) occurred between 36 – 25 Ma. The basement strata were subsequently exhumed at rates of 0.36 – 0.20 mm/yr or 0.28 – 0.16 mm/yr until exposed above sea level by about 11 Ma. Between 11 and 7 Ma, sedimentation of the Mangaoranga Formation occurred. First, northward-flowing braided rivers deposited conglomerate (sm1) in half-grabens. At the Mauriceville and Mangaoranga Stream sites, a large co-seismic lake developed, leading to the sedimentation of interbedded sandstone and mudstone (sm6). The lake persisted for around 95 ky and was often flooded. Eventually, the lake shallowed, and rivers flowed back across the area. The region was subsequently submerged as a marine transgression occurred, leading to the sedimentation of the upper three members of the Mangaoranga Formation (sandstone (sm3), siltstone (sm4) and mudstone (sm5)). Water depths in north-western Wairarapa reached a maximum of 600 ± 300 m by about 8 to 7 Ma. The results of the floral investigation indicate that areas of significant relief were present in north-western Wairarapa during the Late Miocene (possibly up to, or just over, 900 m above sea level). These areas were occupied by cool temperate beech (Nothofagus fusca type) forests, with minor components of Phyllocladus, Podocarpus spp. and Coprosma spp. On low-lying areas, warm temperate beech (Nothofagus brassi type) forests were common, which often contained Laurelia novaezelandiae and Dacrycarpus dacrydioides in areas with impeded drainage and, in areas with better drainage, Dacrydium cupressinum type. In coastal areas, woodland forests of Metrosideros spp. and Casuarinaceae spp. were common. Although no new direct information on the history of north-western Wairarapa between the latest Early Cretaceous and Middle Miocene was determined in this study, the apatite fission-track results suggest that little to no sedimentation occurred in the region between 36 – 25 Ma and 11 Ma, as cooling of the basement strata as a result of uplift and erosion occurred over this time.</p>

Late Miocene paleogeography and flora of north-western Wairarapa, New Zealand

<p>The Late Miocene flora and paleogeography of north-western Wairarapa were determined by examining and sampling the Upper Miocene marine and non-marine deposits of the Mangaoranga Formation. This formation unconformably overlies Mesozoic greywacke basement in areas of north-west Wairarapa and contains the oldest sediments preserved immediately overlying basement in this area. Little work has been carried out previously to fully understand the depositional history of the formation or the surrounding vegetation cover. Thus, the present study is intended to improve interpretations of the Late Miocene paleogeography and flora of north-western Wairarapa. The strata of the Mangaoranga Formation were examined at three locations in north-western Wairarapa: at Mangaoranga Stream (Eketahuna), Central Mangaone Road (Eketahuna) and Mauriceville. For paleogeographic reconstructions, the strata were described at Mangaoranga Stream and subsequently correlated to strata at the Mauriceville and Central Mangaone Road sites. The formation was sampled several times at each site for palynological analysis. Additionally, samples available for pollen analysis from the Mt Bruce and Alfredton areas were also examined. The results of these analyses, in conjunction with mummified leaves, aided reconstructions of the Late Miocene vegetation cover. Fission-track analysis on apatite grains from Torlesse basement immediately below the formation was also undertaken, providing evidence for the cooling (and hence exhumation) and subsequent burial history of the basement strata. The results of the apatite fission-track analysis suggest that exhumation of the basement strata above the apatite closure temperature (110ºC) occurred between 36 – 25 Ma. The basement strata were subsequently exhumed at rates of 0.36 – 0.20 mm/yr or 0.28 – 0.16 mm/yr until exposed above sea level by about 11 Ma. Between 11 and 7 Ma, sedimentation of the Mangaoranga Formation occurred. First, northward-flowing braided rivers deposited conglomerate (sm1) in half-grabens. At the Mauriceville and Mangaoranga Stream sites, a large co-seismic lake developed, leading to the sedimentation of interbedded sandstone and mudstone (sm6). The lake persisted for around 95 ky and was often flooded. Eventually, the lake shallowed, and rivers flowed back across the area. The region was subsequently submerged as a marine transgression occurred, leading to the sedimentation of the upper three members of the Mangaoranga Formation (sandstone (sm3), siltstone (sm4) and mudstone (sm5)). Water depths in north-western Wairarapa reached a maximum of 600 ± 300 m by about 8 to 7 Ma. The results of the floral investigation indicate that areas of significant relief were present in north-western Wairarapa during the Late Miocene (possibly up to, or just over, 900 m above sea level). These areas were occupied by cool temperate beech (Nothofagus fusca type) forests, with minor components of Phyllocladus, Podocarpus spp. and Coprosma spp. On low-lying areas, warm temperate beech (Nothofagus brassi type) forests were common, which often contained Laurelia novaezelandiae and Dacrycarpus dacrydioides in areas with impeded drainage and, in areas with better drainage, Dacrydium cupressinum type. In coastal areas, woodland forests of Metrosideros spp. and Casuarinaceae spp. were common. Although no new direct information on the history of north-western Wairarapa between the latest Early Cretaceous and Middle Miocene was determined in this study, the apatite fission-track results suggest that little to no sedimentation occurred in the region between 36 – 25 Ma and 11 Ma, as cooling of the basement strata as a result of uplift and erosion occurred over this time.</p>

Thermal Maturity of the Grajcarek Unit (Pieniny Klippen Belt): Insights for the Burial History of a Major Tectonic Boundary of the Western Carpathians

The Grajcarek Unit of the Pieniny Klippen Belt (PKB), at the boundary between the Central (Inner) and Outer Carpathians, resulted from the convergence of the ALCAPA (the Alps–Carpathians–Pannonia) block and European plate. The strongly deformed slices of the Grajcarek Unit consist of Jurassic–Cretaceous sedimentary rocks associated with Late Cretaceous–Middle Palaeocene synorogenic wild-flysch, and sedimentary breccias with olistoliths. Maximum burial temperatures and burial depths were estimated based on vitrinite reflectance data. The vitrinite reflectance values were wide scattered through the Grajcarek sedimentary succession, especially in the flysch formations. This is attributed mainly to the depositional effects that affected the vitrinite evolution. The determined maximum burial temperatures were interpreted due to the regional compression controlled by tectonic burial coeval with thrusting and strike-slip faulting. The regional vitrinite reflectance variations might estimate cumulative displacement around the NNW–SSE and oriented the strike-slip Dunajec fault, which is a continuation of the deep fracture Kraków–Myszków fault zone.

Burial History, Hydrocarbon Generation, and Migration in the Upper Paleogene Petroleum System of the Offshore North Sumatra Basin: Insights from 1D and 2D Basin Modeling.

One-dimensional and two-dimensional basin modeling can be used to infer the burial history, hydrocarbon generation, and migration of hydrocarbon. In this paper, the study focuses on 1D and 2D basin modeling in North Sumatera Offshore as one of the prolific deep-water basins in Indonesia. The data consists of 5 exploration wells and 2D seismic data that are vitrinite reflectance, rock-eval data, and bottom-hole temperature. Well data’s have been used to calibrate heat flow and thermal evolution of the basin, while 2D seismic data have been used to support the basin modeling. Based on the result, the basin formed by the collision of the Australian Plate with the Eurasian Plate evolved due to block faulting that caused a pull-apart basin. In the Early Oligocene, changes in the movement of the Indian plate also changed tectonics from subduction to strike-slip fault resulting in Andaman Sea rifting. The southern part of the research area was affected by the Andaman Sea rifting, which caused unconformities in the Middle Miocene. The main generating source rock is the Bampo, Belumai, and Baong Formation, which is predominantly consist of Type III kerogen (gas prone) in the north and Type II/III (mix oil and gas prone) in the South. The timing of petroleum generation may have occurred is in the Early Pliocene. The Early oil generation which occurred simultaneously with the seal rock and may have been migrated to the Middle and Late Miocene reservoir through the faults as a vertical migration pathway. The results of this study allow us to improve the hydrocarbon prospect and reduce exploration risks.

Evolution of diagenetic conditions and burial history in Buntsandstein Gp. fractured sandstones (Upper Rhine Graben) from in-situ δ18O of quartz and 40Ar/39Ar geochronology of K-feldspar overgrowths

In-situ δ18O measured in the quartz overgrowths help identify temperature and fluid origin variations responsible for cementation of the pore network (matrix and fracture) in the Buntsandstein Gp. sandstone reservoirs within the Upper Rhine Graben. The overgrowths record two types of the evolution of δ18O: 1) a monotonous decrease of the δ18Oovergrowth interpreted as linked to an increasing burial temperature and 2) random fluctuations, interpreted as pointing out the injection of allochthonous fluids in faulted areas, on the cementation processes of the pore network (both intergranular and fracture planes). Fluids causing the quartz cementation are either autochthonous buffered in 18O from clay illitisation; or allochthonous fluids of meteoric origin with δ18O below − 5%. These allochthonous fluids are in thermal disequilibrium with the host sandstone. The measured signal of δ18Oovergrowth measured from samples and calculated curves testing hypothetic δ18Ofluid are compared to T–t evolution during burial. This modelling proposes the initiation of quartz cementation during the Jurassic and is validated by the in-situ 40Ar/39Ar dating results obtained on the feldspar overgrowths predating quartz overgrowths. A similar diagenetic history is recorded on the graben shoulders and in the buried parts of the basin. Here, the beginning of the pore network cementation predates the structuration in blocks of the basin before the Cenozoic graben opening.

Deep vs shallow – two contrasting theories? A tectonically activated Late Cretaceous deltaic system in the axial part of the Danish-Polish Trough; a case study from SE Poland

The Danish-Polish Trough – a large Trans-European sedimentary basin stretching from Denmark, through Germany, to south-eastern Poland and even further to the south into Ukraine, had undergone an uplift during the Late Cretaceous, which in consequence resulted in its inversion and development into the Mid-Polish Anticlinorium. In many existing paleotectonic interpretations, SE Poland, i.e. the subsurface San Anticlinorium and the recent-day Roztocze Hills area was included during the Late Cretaceous into the Danish-Polish Trough, representing its axial and most subsiding part. Such a paleotectonic model was the basis for facies and bathymetric interpretations, assuming that upper Cretaceous sediments deposited close to the axial part of the Danish-Polish Trough (e.g. Roztocze) were represented by the deepest facies. Several studies performed in recent years contradict this concept. The growing amount of data indicates that already from the Coniacian-Santonian times, this area was a land-mass rather than the deepest part of the basin – the same is true for the Campanian and Maastrichtian times. Additionally, recent discoveries of cyclic middle Campanian deposits of shallow deltaic origin, along with a decreasing contribution of terrigenous material towards the NE, have led to the adoption of new facies and bathymetric models, being all in opposite to most of the previous interpretations. The new interpretation implies the presence of a land-mass area in the place where formerly the deepest and most subsiding part of the Danish-Polish Trough was located. Here we document in detail the Late Cretaceous deltaic system, i.e. the Szozdy delta developed in the axial part of the Danish-Polish Trough. The middle Campanian deposits which crop out extensively in the middle Roztocze Hills region, close to the village of the Szozdy, exhibits coarsening-upward tripartite cyclothems. The sequence was deposited in a shallow-water, delta front platform setting. Three facies associations have been distinguished: (1) dark grey calcareous mudstone, deposited in prodelta environment, (2) yellow calcareous sandstone unit, interpreted as prograding delta front lobe deposits of fluvially-dominated though wave/tidally influenced setting, and (3) calcareous gaize unit deposited in areas cut-off from the material supply. The sequence as a whole was accumulated by repeated progradation and abandonment of deltaic complexes. This interpretation is supported by the new sedimentological, palynofacies, and heavy mineral data. The latter is also discussed in the context of their possible source rock provenance, which might suggest a different burial history than thought so far. The development of the Szozdy delta system is placed next to dynamic tectonic processes operating at that time in SE Poland, i.e. the inversion on the one hand, and the generation of new accommodation space for the deltaic deposits by enhanced subsidence. This discovery shed new light on our understanding of facies distribution, bathymetry, paleogeography, and paleotectonic evolution of the south-easternmost part of the inverting Danish-Polish Trough into the Mid-Polish Anticlinorium during the Late Cretaceous times.