Revision of Pressure Transient Analysis in Mature Condensate-Rich Tight Gas Fields in Sultanate of Oman

Pressure transient analysis (PTA) has been used as one of the important reservoir surveillance tools for tight condensate-rich gas fields in Sultanate of Oman. The main objectives of PTA in those fields were to define the dynamic permeability of such tight formations, to define actual total Skin factors for such heavily fractured wells, and to assess impairment due to condensate banking around wellbores. After long production, more objectives became also necessary like assessing impairment due to poor clean-up of fractures placed in depleted layers, assessing newly proposed Massive fracturing strategy, assessing well-design and fracture strategies of newly drilled Horizontal wells, targeting the un-depleted tight layers, and impairment due to halite scaling. Therefore, the main objective of this paper is to address all the above complications to improve well and reservoir modeling for better development planning. In order to realize most of the above objectives, about 21 PTA acquisitions have been done in one of the mature gas fields in Oman, developed by more than 200 fractured wells, and on production for 25 years. In this study, an extensive PTA revision was done to address main issues of this field. Most of the actual fracture dynamic parameters (i.e. frac half-length, frac width, frac conductivity, etc.) have been estimated and compared with designed parameters. In addition, overall wells fracturing responses have been defined, categorized into strong and weak frac performances, proposing suitable interpretation and modeling workflow for each case. In this study, more reasonable permeability values have been estimated for individual layers, improving the dynamic modeling significantly. In addition, it is found that late hook-up of fractured wells leads to very poor fractures clean out in pressure-depleted layers, causing the weak frac performance. In addition, the actual frac parameters (i.e. frac-half-length) found to be much lower than designed/expected before implementation. This helped to improve well and fracturing design and implementation for next vertical and horizontal wells, improving their performances. All the observed PTA responses (fracturing, condensate-banking, Halite-scaling, wells interference) have been matched and proved using sophisticated single and sector numerical simulation models, which have been incorporated into full-field models, causing significant improvements in field production forecasts and field development planning (FDP).

Hydraulic Fracturing to Successfully Exploit Depleted Gas Reserves: A Case History from the North Sea

Hydraulic fracturing has been well established in the Southern North Sea (SNS) since the mid-1980s; however, it has typically been conducted as the final phase of development in new gas fields. One of these fields is Chiswick located in the Greater Markham area 90 miles offshore UK in 130 ft of water. Following an unsuccessful well repair of the multi-fractured horizontal well C4, it was decided to cost-effectively and expediently exploit the remaining pressure-depleted reserves near the toe via a single large fracture initiated from a deviated sidetrack wellbore designated C6. A deviated wellbore was chosen versus the original near-horizontal well to reduce well risk and costs and ultimately deliver an economic well. Several key challenges were identified, and mitigating measures were put in place. Modular formation dynamics tester data from the sidetrack open hole indicated the reservoir pressure gradient had depleted to 0.23 to 0.25 psi/ft, raising concerns about the ability of the well to unload the fluid volumes associated with a large fracture treatment. Wellbore deviation and azimuth with the associated potential for near-wellbore tortuosity would drive a typically short perforation interval (i.e., 3 ft). However, a compromise to mitigate convergent pressure loss in depletion was required, and the perforation interval was therefore set at 14 ft with provision made for robust step-down tests (SDT) and multi-mesh sand slugs. To further offset any near-well convergence pressure drop during cleanup, an aggressive tip screenout (TSO) proppant schedule, including a high concentration tail-in (12 PPA) with an aggressive breaker schedule, was executed to fully develop propped hydraulic width. Following formation breakdown and SDT to 40 bbl/min, the well went on near-instantaneous vacuum. Clearly, an extremely conductive feature had been created or contacted. However, upon use of a robust crosslinked gel formulation and 100-mesh sand, the bottomhole and positive surface pressure data allowed a suitable fracture design to be refined and placed with a large width, as evidenced by the extreme 2,309-psi net pressure development over that of the pad stage while placing 500,500 lbm of 16/30 resin-coated (RC) intermediate strength proppant (ISP) to 12 PPA. Although a lengthy nitrogen lift by coiled tubing (CT) was planned, the well cleanup response in fact allowed unaided hydrocarbon gas flow to surface within a short period. The well was then further beaned-up under well test conditions to a flow rate of approximately 26 MMscf/D under critical flowing conditions with a higher bottomhole flowing pressure than that of the original C4 well. Given the last producing rate of the original multiple fractured horizontal wellbore was 27 MMscf/D at a drawdown of 1,050 psi through two separate hydraulic fractures, then the outcome of this well was judged to be highly successful and at the limit of predrill expectations. This case history explains and details the rationale, methods, and techniques employed in well C6 to address the challenge of successful hydraulic fracture stimulation in a depleted formation. Challenges were addressed by combining a number of techniques, coupled with field experience, resulting in a highly productive well despite the relatively low reservoir pressure coupled with a limited time frame to plan and execute. These techniques are transferrable to other offshore gas fields in the region where reservoir depletion makes economic recovery difficult or indeed prohibitive.

Determination of the Most Interconnected Sections of Main Gas Pipelines Using the Maximum Clique Method

This article is devoted to the definition of the most important combinations of objects in critical network infrastructures. This study was carried out using the example of the Russian gas transmission network. Since natural gas is widely used in the energy sector, the gas transmission network can be exposed to terrorist threats, and the actions of intruders can be directed at both gas fields and gas pipelines. A defender–attacker model was proposed to simulate attacks. In this model, the defender solves the maximum flow problem to satisfy the needs of gas consumers. By excluding gas pipelines, the attacker tries to minimize the maximum flow in the gas transmission network. Russian and European gas transmission networks are territorially very extensive and have a significant number of mutual intersections and redundant pipelines. Therefore, one of the approaches to inflicting maximum damage on the system is modeled as an attack on a clique. A clique in this study is several interconnected objects. The article presents the list of the most interconnected sections of main gas pipelines, the failure of which can cause the greatest damage to the system in the form of a gas shortage among consumers. Conclusions were drawn about the applicability of the maximum clique method for identifying the most important objects in network critical infrastructures.

The influence of trap magmatism on the creation of oil and gas deposits

The need to maintain the level of production and an acceptable cost of developing oil and gas fields forces us to rely primarily on the existing reserve, that is, to maximize the potential of traditional oil and gas production regions and adjacent territories - the marginal zones. At the same time, it is necessary to develop unexplored sedimentary complexes at depths of more than 3-5 km. Against this background, it is necessary to highlight a special phenomenon that increases the oil and gas potential of the subsoil associated with trap magmatism. The insufficient level of knowledge of the subsoil makes it possible to predict the discovery of large oil and gas deposits of the traditional type, which will ensure their high profitabilitye. Keywords: trap magmatism; profitability of oil and gas resources; marginal zones; hornfels; transformation of carbonates; rocks of trap formations; regional seals.

Structural changes in the economy of the Northern zone in the modern period

The aim of the work was to study and evaluate structural changes in the economy of the regions of the North at the present stage of their development (in the period from 2015 to 2019). On the basis of the methodology previously developed by the author for assessing structural shifts, twenty types of economic activity were grouped into two large spheres: production and non-production (services), each consisting of four combined industries. For these economic spheres and industries, an assessment of sectoral and then territorial structural shifts in the period 2015–2019 was carried out. It was found that in the structure of the economy of the regions of the North during this period, the vector of development changed towards an increase in the share of the production sector and a decrease in the non-production sector by 4,4 %, whereas in the previous period 2005–2015, the opposite picture was observed. The high rates of development of the production sector in all regions of the North were revealed, while it grew most rapidly in the West Siberian region due to the extensive development of new gas fields and the construction of new largest LNG complex in the North on the Yamal Peninsula. As a result, the share of GRP in the Northern zone increased in the country from 13,2 % in 2015 to 14,5 % in 2019, and the pace of development was outstripping: 144,6 % versus 129,2 % in the Russian Federation. It is noted that the pace and volume of both sectoral and territorial structural shifts in the production sector in almost all regions of the North zone are almost entirely related to both the scale of investments directed to the development of their economy and the current situation for their resources in the world commodity markets.

Determining factors of the unconsolidated rocks of Cenomanian reservoir on the Bolshekhetskaya depression

The relevance of the article is associated with the importance of the object of the research. Dozens of unique and giant oil and gas fields, such as Urengoyskoye, Medvezhye, Yamburgskoye, Vyngapurovskoye, Messoyakhskoye, Nakhodkinskoye, Russkoye, have been identified within the Cenomanian complex. The main feature of Cenomanian rocks is their slow rock cementation. This leads to significant difficulties in core sampling and the following studies of it; that is the direct and most informative source of data on the composition and properties of rocks that create a geological section.The identification of the factors, which determine the slow rock cementation of reservoir rocks, allows establishing a certain order in sampling and laboratory core studies. Consequently, reliable data on the reservoir and estimation of hydrocarbon reserves both of discovered and exploited fields and newly discovered fields that are being developed on the territory of the Gydan peninsula and the Bolshekhetskaya depression will be obtained. This study is also important for the exploration and development of hydrocarbon resources of the continental shelf in the waters of the Arctic seas of Russia as one of the most promising areas.As a result of the analysis, it was found that the formation of rocks of the PK1-3 Cenomanian age of the Bolshekhetskaya depression happened under conditions of normal compaction of terrigenous sedimentary rocks that are located in the West Siberian basin. Slow rock cementation of reservoir rocks is associated with relatively low thermobaric conditions of their occurrence, as well as the low content of clay and absence of carbonate cements. Their lithological and petrophysical characteristics are close to the analogous Cenomanian deposits of the northern fields of Western Siberia and can be applied to other unconsolidated rocks studied areas.

An investigation of methods for calculating the volume of methane dissolved in reservoir water

Existing gas production technologies limit gas recovery at the level of 85 %. Therefore, it is important to introduce technologies that make it possible to maximize the volume of production and intensify the inflow; for their selection it is important to have a reliable estimate of the residual gas reserves, since with a significant volume of the aquifer of gas fields, the volume of dissolved gas can be up to 10 % of the total reserves of the reservoir, which should be taken into account when designing the application of technologies to increase gas recovery.The main hydrocarbon dissolving in reservoir water is methane. In this regard, it is of interest to study methods that make it possible to determine the volume of hydrocarbon gases dissolved in saline water, which will make it possible to determine the total reserves of such gas. We investigated the existing methods for calculating the amount of methane dissolved in reservoir water, and gave a quantitative assessment of the volume of gas dissolved in water.

The geosolitonic concept of high output hydrocarbon deposits formation

Based on the well-known results of studies of the ether-geosoliton concept of the growing Earth, the article presents the conclusions that made it possible to propose a model of thermonuclear synthesis of chemical elements that form renewable reserves of developed oil and gas fields. It was revealed that local zones of abnormally high production rates of production wells and, accordingly, large cumulative production at developed fields in Western Siberia are due to the restoration of recoverable reserves due to geosoliton degassing. Therefore, when interpreting the results of geological and geophysical studies, it is necessary to pay attention to the identified geosoliton degassing channels, since in the works of R. M. Bembel and others found that they contributed to the formation of a number of hydrocarbon deposits in Western Siberia. When interpreting the results of geological-geophysical and physicochemical studies of the fields being developed, it is recommended to study the data of the ring high-resolution seismic exploration technology in order to identify unique areas of renewable reserves, which can significantly increase the component yield of hydrocarbon deposits.