Genesis of Coalbed Methane and Its Storage and Seepage Space in Baode Block, Eastern Ordos Basin

The Baode block on the eastern margin of the Ordos Basin is a key area for the development of low-rank coalbed methane (CBM) in China. In order to find out the genesis of CBM and its storage and seepage space in Baode block, the isotopic testing of gas samples was carried out to reveal the origin of CH4 and CO2, as well, mercury intrusion porosimetry, low temperature nitrogen adsorption, and X-ray CT tests were performed to characterize the pores and fractures in No. 4 + 5 and No. 8 + 9 coal seams. The results showed that the average volume fraction of CH4, N2, and CO2 is 88.31%, 4.73%, and 6.36%, respectively. No. 4 + 5 and No. 8 + 9 coal seams both have biogenic gas and thermogenic methane. Meanwhile, No. 4 + 5 and No. 8 + 9 coal seams both contain CO2 generated by coal pyrolysis, which belongs to organic genetic gas, while shallow CO2 is greatly affected by the action of microorganisms and belongs to biogenic gas. The average proportion of micropores, transition pores, mesopores, and macropores is 56.61%, 28.22%, 5.10%, and 10.07%, respectively. Samples collected from No. 4 + 5 coal seams have developed more sorption pores. Meanwhile, samples collected from No. 8 + 9 coal seams exhibited a relatively low degree of hysteresis (Hg retention), suggesting good pore connectivity and relatively high seepage ability, which is conducive to gas migration. The connected porosity of coal samples varies greatly, mainly depending on the relative mineral content and the proportion of connected pores.

Dynamic Modeling Workflow for an Unconventional Biogenic Gas Reservoir with Multistage Hydraulic Fracture. A Case Study of Miocene Gachsaran Formation, Abu Dhabi, United Arab Emirates

The Miocene Gachsaran Formation across Onshore Abu Dhabi and Dubai possesses high potential of generating shallow biogenic gas. A dynamic model and field development plan generated based on a detail G&G analysis to understand and evaluate its capability as promising gas resources. Specific approaches and workflow generated for volumetric and dynamic reservoir model capable of defining the most viable development strategy of the field from both an economic and technical standpoint. The proposed workflow adapts also the development plan from single pad-scale to full field development plan. A fine-grid field-scale with more than hundreds of Pads covering the sweet spot area of three thousands of square kilometers including structure, reservoir properties built based on existing vertical wells, newly drilled horizontal wells and seismic interpretation. In this paper, a robust workflow for big and complex unconventional biogenic gas reservoir modeling and simulation technique have been developed with hydraulic fracture and stimulated area created through LGR. Independent workflows generated for the adsorbed gas in place calculation, desorption flow mechanism, and Pads field development plan. An accuracy on in place calculation, desorption flow mechanism and Pseudo steady state flow through direct and indirect total gas concentration measured using (1) Pressurize core and sorption isotherm capacity experiment, (2) Langmuir /BET function and Vmax scaling curves for each grid cells, and (3) Gas concentration versus TOC relationship. Field development plan for unconventional shallow biogenic gas reservoirs is possible only if a communication network created through hydraulic fractures connects a huge reservoir area to the wellbore effectively. A complete workflow presented for modeling and simulation of unconventional reservoirs, which in-corporates the characterization of hydraulic fracture and their interaction with reservoir matrix. Dual porosity model has been constructed with accurate in place calculation through scaling the Langmuir function and calculation Vmax for each grid cell of the full field model, The single Pad design approach in the development plan has exhibited great advantages in terms of improvement in the quality and flexibility of the model, reduction of working time with the same Pad model design which is adapted for the full field development plan. The proposed unconventional modeling and field development plan workflow provides an efficient and useful unconventional dynamic model construction and full field development planning under uncertainty analysis. Minimizing the uncertainty in place calculation and production forecasting for unconventional reservoirs necessitates an accurate direct and indirect data measurement of gas concentration and flow mechanism through the laboratory measurement. Field development plan for unconventional reservoirs is possible only if fracture network can be created through hydraulic fractures that connects a huge reservoir area to the wellbore effectively through pad completion.

Evaluation of Gas Generation Potential Using Thermal Maturity Modelling—The Katakolo Case: A Probable Pathway to Energy Transition

It is evident that the increased focus on energy transition, will increase the demand for gas as it is the transitional fuel to the net zero CO2 emission era. The West Katakolo field is the only oil and gas discovery in Western Greece, and it is operated by Energean. The three offshore West Katakolo wells have defined both the oil and the gas zones, while onshore exploration wells have penetrated biogenic gas-saturated Plio-Pleistocene sands. This study assesses the gas generation potential of the local Plio-Pleistocene and Triassic sources using thermal maturity modelling based on the available legacy data, with limitations being addressed by running several case-scenarios. In conclusion, this study supports the generation of thermogenic and biogenic gas from the Triassic and Plio-Pleistocene sources respectively, demonstrating the importance of maturity modelling in hydrocarbon exploration, applied on the Katakolo case; a potential gas source to facilitate the energy transition in Greece.

Managed Pressure Drilling and Underbalanced Drilling Compounded Role in Solving the Exploration and Appraisal Challenges of Biogenetic Gas Resources in the United Arab Emirates -Case Study

Biogenic gas resources have gathered importance recently due to its widespread availability, occurrence at geologically predictable circumstances, and existence at shallow depths. It is estimated that biogenic gas forms more than 20% of the global discovered reserves. However, the exploration and development of these unconventional resources come with numerous drilling and reservoir challenges. This paper showcases a novel approach used in the United Arab Emirates to overcome these challenges using managed pressure and underbalanced drilling. To tackle both reservoir and drilling challenges, a hybrid solution combining Underbalanced (UBD) and Managed Pressure Drilling (MPD) was applied. UBD was used to characterize the reservoir in terms of pressure and productivity index to ultimately enhance productivity by eliminating formation damage. MPD was used next to continue drilling through the problematic zone which had high instability due to the presence of highly sensitive salt, in addition to the presence of high pressure and loss zones. The fit for purpose hybrid application design allowed the operator to immediately switch between UBD and MPD conditions, as the well required with the same equipment. Three of the four targeted formations were in the 8 ½″ hole section, UBD was selected to drill the first reservoir formation which allowed pore pressure verification and avoided using excessive mud weight that was the culprit of many challenges like slow ROP, drilling fluid losses, bit balling, and fracking the formations. UBD has proved that mud weight can be reduced by 20%-30% comparing to conventional drilling. The second formation was a salt formation that has caused previously hole collapse and losses-kicks problems as heavy mud used to drill this salty formation. MPD used successfully drill this section by constant bottom hole pressure and lower mud weight as it was found from analyzing offset wells reports that hole collapse occurred at connections and pump off events. Constant Bottom Hole Pressure (CBHP) also eliminated tight spots and excessive reaming resulting in optimized drilling. The third formation used MPD as well to minimize overbalance pressure over previous sections while the fourth formation was drilled by UBD as it had a separate 6″ hole section as it formed an independent reservoir. The combined MPD and UBD approach eliminated most the NPT encountered in offset wells, enhanced Rate of Penetration (ROP) by 200% to 300% and slashed the well drilling time by 27 days.

Depositional sequence interpretation using seismic and well data of offshore Central Sumatra Basin

Offshore Central Sumatra Basin is an integral part of Central Sumatra Basin known for producing hydrocarbon basins. The derivation of stratigraphic study of seismic and well data is intended to improve accuracy of geological interpretation. Sequence stratigraphy studies have a significant role in exploratory studies to determine which depositional sequence can be inferred as hydrocarbon reservoir and its correlation in petroleum system. This study aims to identify biogenic gas sequential interpretation using seismic and well data of offshore Central Sumatra Basin. The procedure to analyze sequence stratigraphy is to identify stratigraphy surface markers using GR log, then map these markers to the seismic section that has been tied with good data to determine the distribution of each stratigraphy sequence. This study area has five depositional sequences, which are predominantly formed in marine depositional environments. Potential source rock in this area is at DS-1 which has a lacustrine depositional environment with euxinic conditions. The euxinic shale at the upper TST-1 deposit could be a source rock with hydrocarbon migration through faults. Biogenic gas reservoir potential is in Petani Formation (DS-5). Shale in MFS-5 and HST-5 could be a hydrocarbon trap, whereas LST-5 and TST-5 sandstone deposits can be a reservoir.

Basins Analysis and Petroleum Systems Modeling of Western Black Sea, Ukrainian Sector

The Ukrainian sector of the Western Black Sea (WBS) is one of the last remaining exploration frontiers in Europe. This area, which includes shelf to deepwater environments, is underexplored with no drilling of targets in water depths exceeding 100 meters. That is why, the Ukrainian sector of the WBS is attractive for exploration, especially in the context of new play types and targets such as biogenic gas. These hydrocarbon formations have been proven by neighboring Romania and Turkey in the areas adjacent to Ukrainian waters. Therefore, a rigorous Basin Analysis program has been initiated to assess the petroleum systems and play risks in the entire Ukrainian sector of the WBS. The goals of this program are: 1) to establish a regional geoscience foundation following best industrial practices in exploration; 2) to enable establishing more accurate risking and ranking procedures for an exploration portfolio and 3) to provide critical support for the analysis of a new generation of seismic data that is currently being acquired. In this paper the initial scope of work is presented.

Structure, Faulting and Gas Accumulation: Southeast Wanganui Basin, New Zealand

<p>There has been low interest in petroleum exploration in the Wanganui Basin as it lacks known hydrocarbon source rock of sufficient age or burial depth. However, the onshore Southeast Wanganui Basin has many occurrences of methane-rich biogenic gas found in shallow water wells. This project used three studies across the Horowhenua area to examine the faulting style in the Southeast Wanganui Basin where it is bounded by the Tararua range- front, and how this faulting relates to the accumulation of gas deposits in the shallow sedimentary section. South of Levin the Tararua range front steps laterally near Muhunoa East Road. A previous seismic reflection line identified a deep intra-basement arrival, which could have been either a low-angle thrust fault or side-swipe from a pull-apart basin at the step in the Tararua range front. Two seismic lines and a gravity survey found no sub-vertical drops in basement depth which would indicate the presence of a pull-apart basin or a favourable surface off which a laterally travelling seismic wave could reflect. The intra-basement arrival on the previous seismic line was therefore interpreted to be from an intra-basement low-angle thrust fault. Also two biogenic gas sites also were surveyed. A shallow gas reservoir east of Levin on Wallace Road, abutting the Tararua range front, had been discovered when a water well was drilled; and a potential reservoir southwest of Sanson was located when an aerial survey identified a domed structure with high resistivity. In both areas biogenic gas was thought to be trapped in buried sand dunes at a depth of approximately 20 m. Shallow seismic refraction and reflection methods and amplitude variation with offset analysis were used to map both reservoir bodies and confirm the presence of biogenic gas.</p>

Structure, Faulting and Gas Accumulation: Southeast Wanganui Basin, New Zealand

<p>There has been low interest in petroleum exploration in the Wanganui Basin as it lacks known hydrocarbon source rock of sufficient age or burial depth. However, the onshore Southeast Wanganui Basin has many occurrences of methane-rich biogenic gas found in shallow water wells. This project used three studies across the Horowhenua area to examine the faulting style in the Southeast Wanganui Basin where it is bounded by the Tararua range- front, and how this faulting relates to the accumulation of gas deposits in the shallow sedimentary section. South of Levin the Tararua range front steps laterally near Muhunoa East Road. A previous seismic reflection line identified a deep intra-basement arrival, which could have been either a low-angle thrust fault or side-swipe from a pull-apart basin at the step in the Tararua range front. Two seismic lines and a gravity survey found no sub-vertical drops in basement depth which would indicate the presence of a pull-apart basin or a favourable surface off which a laterally travelling seismic wave could reflect. The intra-basement arrival on the previous seismic line was therefore interpreted to be from an intra-basement low-angle thrust fault. Also two biogenic gas sites also were surveyed. A shallow gas reservoir east of Levin on Wallace Road, abutting the Tararua range front, had been discovered when a water well was drilled; and a potential reservoir southwest of Sanson was located when an aerial survey identified a domed structure with high resistivity. In both areas biogenic gas was thought to be trapped in buried sand dunes at a depth of approximately 20 m. Shallow seismic refraction and reflection methods and amplitude variation with offset analysis were used to map both reservoir bodies and confirm the presence of biogenic gas.</p>