Dynamics Of Hydrocarbon Accumulation In The Northern Bonaparte Basin, Australia

The northern Bonaparte Basin encompasses the area to the northwest of the Petrel Sub-basin containing a thick Mesozoic and Cenozoic succession. The region is rich in hydrocarbon resources especially natural gas and condensate, including Evans Shoal, Evans Shoal South, Blackwood, Caldita, Barossa (Lynedoch), Chuditch, and Sunrise-Troubadour gas fields, which have recoverable volumes reserves of 8.3,0.07,2.5,2.9, 2.7,0.7 and 5.5 Tcf (Trillion cubic feet), respectively.The data from the wells Beluga 1, Evans Shoal 1, Evans Shoal 2, Heron 1, Lynedoch 1, Lynedoch 2, Loxton Shoals 1, Sunset 1, Chuditch 1, Troubadour 1, Sunrise 1, Sunrise 2, and Seismic Lines N 11606, N 11805 and N 11809 in the northern Bonaparte Basin located in the north east of Bonaparte Basin, Australia were selected to study the dynamics of hydrocarbon accumulation in the study area. Basin Mod 1-D,2-D, and 3-D softwares were used for modeling. The geothermal gradient values range from 3.05℃/100 m to 5.72℃/100 m with an average of 4.12℃/100 m and the present-day heat flow values change from 46.23 to 75.85 mW/m2 with an average of 61 mW/m2. The highest geothermal gradient and present-day heat flow values occurred in the Sahul Platform, these most likely indicate that hot fluids are currently variably migrating into this structure. The lower geothermal gradient and heat flow values have been modelled in the southeast sites in the well Beluga 1. The northern Bonaparte Basin experienced several deformation phases including lithospheric thinning; hence, the heat flow is expected to vary over the geological history of the basin. The higher paleo-heat flow values changing from 83.54 to 113 mW/m2 with an average of 104.16 mW/m2 during Jurassic rift event (syn-rift) were sufficient for source rocks maturation and hydrocarbon generation throughout Cretaceous post-breakup sequence (post-rift) in the study area.Analyse organic matter showed that the Lower-Middle Jurassic to Lower Cretaceous source rocks in the study area were gas prone with kerogen type III predominantly, except in the Echuca Shoals Formation of well Troubadour 1 was none gas-prone with kerogen type Ⅳ. And also in the Tuatara (Upper Frigate) Formation of the well Beluga 1, in the Elang and Echuca Shoals formations of the well Sunsetl, and in the Elang Formation of the well Troubadour 1 were mixed oil- and gas-prone with kerogen type II&III predominantly. In the Malita Graben and Sahul Platform, the source rock richnesses and hydrocarbon potential generation changed from poor-to-very good, respectively, and in the Calder graben, they changed from fair-to-very good and poor-to-fair, respectively. In the Malita Graben the source rocks varied from early to high maturity level, and in the Calder Graben, they were high maturity level, whereas in the Sahul Platform, they changed from early to mid-mature oil, except in the well Loxton Shoals 1 changed from middle to late mature oil.In the well Beluga 1, the oil and gas generated from the Plover and Tuatara (Upper Frigate) formations source rocks started in the Late Cretaceous and expelled during the Middle Paleogene and Early Neogene, respectively. The amount of oil generated from the Plover and Tuatara (Upper Frigate) formations were 15.10 and 21.16 mg/g TOC and gas were 33.36 and 13.28 mg/g TOC with an expelling efficiencies of oil were 3.48 and 21.79% and gas were 26.53 and 21.46%, respectively. In the well Heron 1, the oil and gas generated from these Petrel (Frigate) and Echuca Shoals formations started at Early and Middle Cretaceous, and expelled during Late Cretaceous (Turonian age) and Late Paleogene, respectively. The amount of gas generated from these two formations were 36.29 and 26.77 mg/g TOC, and oil were 15.30 and 11.95 mg/g TOC with an expelling efficiencies of gas were 72.38 and 34.35%and oil ones were 60.43 and 31.71%, respectively. In the well Evans Shoal 1, the oil and gas generated from Plover, Cleia (Lower Frigate), and Echuca Shoals formations started at the Late Cretaceous, and expelled at Late Cretaceous for Plover Formation and at Late Paleogene for Cleia and Echuca Shoals formations, respectively. The amount of gas generated from these three formations are 66.98,18.89 and 14.29 mg/g TOC and oil are 29.55,8.22 and 6.13 mg/g TOC with an expelling efficiencies of gas were 72.54,39.60 and 37.93%and oil were 71.54,37.96 and 37.36%, respectively. The oil and gas generated from the Plover Formation source rock in the well Evans Shoal 2 began in the Middle Cretaceous and from the Cleia (Lower Frigate) and Echuca Shoals formations source rocks, in the same well, commenced in the Late Cretaceous and expelled at the Late Cretaceous, respectively. The amount of gas generated from these three formations were 63.84,57.34 and 65.73 mg/g TOC and oil were 25.16,23.91, and 27.88 mg/g TOC with expelling efficiencies of gas were 47.56,50 and 52.26%and oil were 32.43,37.68 and 40.82, respectively. The oil and gas generated from the Cleia (Lower Frigate) and Echuca Shoals formations source rocks in the well Lynedoch 1 started at Late Cretaceous and expelled at Late Paleogene and Early Neogene, respectively. The amount of generated oil from these two formations were 12.33 and 10.92 mg/g TOC, and gas were 28.35 and 25.16 mg/g TOC with expelling efficiencies of oil were 8.97 and 24.54%and gas were 10.91 and 28.22%, respectively. The oil and gas generated from the Plover, Elang, and Echuca Shoals formations source rocks in the well Lynedoch 2 began at the Late Cretaceous, and expelled at Early Neogene from the Plover and Elang formations and during Early Paleogene from the Echuca Shoals Formation.The amounts of oil generated from these three formations were 13.75,14.09, and 19.73 mg/g TOC and gas were 35.15,34.77, and 46.85 mg/g TOC with expelling efficiencies of oil were 6.04,8.80 and 43.08%and gas were 18.07,17.10 and 50.50%, respectively. In the well Loxton Shoals 1, the threshold of oil and gas generated of the Plover and Laminaria formations source rocks were occurred during the Late Cretaceous and Middle Paleocene, and expelled at the Pleistocene, respectively. The amount of generated oil from these two formations were 14.28 and 19.10 mg/g TOC and gas were 31.38 and 42.30 mg/g TOC with expelling efficiencies of oil were 4.90 and 34.71%and gas were 5.10 and 34.42%, respectively.In the well Sunset 1, the oil and gas generated from the Plover Formation source rock started during Early Paleogene and from Elang, and Echuca Shoals formations source rocks during Middle Paleogene, and expelled at the Pleistocene, respectively. The amount of generated oil from these three formations were 7.27,17.38, and 21.57 mg/g TOC and gas were 16.17,3.57, and 4.25 mg/g TOC with expelling efficiencies of oil were 8.53, 53.62 and 60% and gas were 8.47,51.82 and 59.06%, respectively. The beginning of oil and gas generated from the Plover, Elang and Echuca Shoals formations source rocks in the well Troubadour 1 started at the Late Cretaceous, and expelled from Plover and Elang formations at Early and Late Neogene, respectively. Nil hydrocarbon expelled from Echuca Shoals Formation. The amounts of oil generated from these three formations were 8.61,6.96, and 0.62 mg/g TOC and gas were 18.95,15.48, and 1.36 mg/g TOC with expelling efficiencies of gas from these three formations were 44.33,38.57 and 0.00% and oil were 44.13,38.51 and 0.00%.Oil and gas generated from the Plover, Flamingo (Upper Frigate) and Echuca Shoals formations source rocks in the well Chuditch 1 began at the Late Cretaceous, and expelled at Middle Eocene, Late Pliocene, and Early Miocene, respectively. The amounts of oil generated from these three formations were 17.19,16.98, and 13.27 mg/g TOC and gas were 37.95,37.53, and 29.32 mg/g TOC with expelling efficiencies of oil were 73.30,2.18 and 50.87%and gas ones were 73.73,2.21 and 51.09%, respectively.The Middle Jurassic Plover Formation sandstone reservoir in the Sunset-Loxton Shoals field overlain by the claystones of the Elang (Laminaria), Echuca Shoals, and Wangarlu formations effective seal rocks was a poor-to-very good quality and potential for gas beds, whereas it overlain by the claystones of the Flamingo, Echuca Shoals, and Wangarlu formations effective seal rocks was a very poor-to-very good quality and potential for gas beds in the Chuditch field. In the Evans Shoal field the MiddleJurassic Plover Formation sandstone reservoir overlain by the claystones of the Cleia (Lower Frigate), Echuca Shoals, and Wangarlu formations effective seal rocks was low porosity and good permeability for gas bed and it overlain by the claystones of the Elang, Echuca Shoals, and Wangarlu formations effective seal rocks was poor quality and low potential reservoirin the Lynedoch field.The main conduit systems for migration pathways in the northern Bonaparte Basin were fractures, permeable bed of sandstones, unconformities, and faults.The intensities of gas generation and expulsion were more than of oil ones either in the Sahul Platform or in the Malita and Calder Grabens. During the Late Cretaceous at 66 Ma, hydrocarbon migrated mainly from the Upper Jurassic Petrel (Frigate) Formation source rock in the Malita Graben depocentre (structurally lower) to the Plover Formation sandstone reservoir in the Sunset-Loxton Shoals field. In the Chuditch field, the hydrocarbon migration to the Plover Formation sandstone reservoir was initiated during the Late Miocene at 7.5 Ma from the Middle Jurassic Plover Formation source rock in the well Chuditch 1. At the present day, in the Sunset-Loxton Shoals field, the hydrocarbon migration to the Plover Formation reservoir overlain by the claystones of the Elang (Laminaria), Echuca Shoals, and Wangarlu formations effective seal rocks started during the Late Cretaceous, plus at the Middle Paleogene from the Middle Jurassic Plover Formation source rock in the well Chuditch 1and at the Late Paleogene from the Early Cretaceous Echuca Shoals Formation source rock in the well Heron 1, and at the Early Neogene from the Early Cretaceous Echuca Shoals Formation source rock in the well Chuditch 1 (structurally lower). In the Chuditch field, the hydrocarbon migration to the Plover Formation reservoir overlain by the claystones of the Flamingo, Echuca Shoals, and Wangarlu formations effective seal rocks was initiated during the Late Miocene from the Middle Jurassic Plover Formation source rock in the well Chuditch 1, as well as from the Upper Jurassic Petrel (Frigate) and Lower Cretaceous Echuca Shoals source rocks formations in the Malita Graben.The main migration pathways were from the south eastward and southward of the Sunrise-Loxton Shoals field, and from southward and eastward of the Chuditch field, precisely from the hydrocarbon source kitchens of the Malita Graben depocentre. The traps in the Sahul Platform have been effective to receive the migrated hydrocarbons. The Sunset-Loxton Shoals trap was identified with filled area of 2076 km2 and available pore volume of 5.34x1011 bbls, whereas the volumes of hydrocarbon entered, accumulated and spilled were 2.83×1012 bbls,5.34×1011 bbls and 2.29×1012 bbls, respectively. However, the mass of maximum hydrocarbon potential, hydrocarbon entered, accumulated and hydrocarbon spilled from the trap were 5.70 x 1013 kg,2.91×1014 kg,5.70×1013 kg, and 2.34×1014 kg respectively. The Chuditch trap was known as a filled area of 981.30 km2 and available pore volume of 3.33x1010 bbls, whereas the volumes of hydrocarbon entered, accumulated and spilled were 2.60x1012 bbls,3.33x1010 bbls and 2.57x1012 bbls, respectively. However, the mass of maximum hydrocarbon potential, hydrocarbon entered, accumulated and hydrocarbon spilled from the trap were 3.44×1012 kg,2.69×1014kg,3.44×1012 kg, and 2.66×1014 kg respectively.