Sequence Stratigraphy of the Fatha Formation in Shaqlawa Area, Northern Iraq

A surface section of the Fatha Formation (Middle Miocene) was studied in the Shaqlawa area, Erbil, Northern Iraq. It consists of siliciclastic silt, evaporates, and carbonates in a mixed siliciclastic silt composition. The Fatha Formation in the study area can be divided into two members of variable thickness based on rocky differences. Depositional settings ranged from shallow open-marine and restricted-hypersaline to supratidal and continental (sabkha, fluvio-deltaic, and exposure). It is bounded below by a type one sequence boundary above the Eocene Pila Spi Formation and marked by conglomerates. The upper sequence boundary with the Injana Formation is conformable. Thirteen sedimentary facies were distinguished in the Fatha Formation within the Shaqlawa region of northern Iraq and include sandstone to mudstone, wavy bedded sandstone to mudstone, Flaser bedded sandstone to mudstone, Marl, sandstone, cross lamination sandstone, Trough cross bedded sandstone, Planar cross bedded sandstone, marly limestone lithofacies, bioclastic grainstone to packstone microfacies, bioclastic lime mudstone to wackestone microfacies, lime mudstone-wackestone microfacies, and gypsum lithofacies. The depositional environment of the formation was inferred based on the facies association concepts. The succession formation can be divided into several third-order cycles, which reflect fluctuations in the relative sea-level rise. High-frequency cycles of transgressive System Tract and Highstand System tract. Fundamental to the evolution of the sequence, in this case, is the local tectonic component.

Casing While Drilling Successfully Implemented for the First Time in High Risk Area of the Bahrain Field

One known risk of the Awali field is hole collapsing in the surface section due to the presence of floating bloulders and cavities in areas of the field; resulting in wells being abandoned as conventional drilling was not enough to solve this issue. In 2019, Schlumberger and Tatweer Petroleum combined forces to improve production of Ostracod/Magwa shallow reservoirs by drilling wells in new areas of the field which included drilling in locations with offset wells that were abandoned due to hole collapse issues in the first 500’ interval. Drilling campaign started in june 2019 and drilled succesfully two wells, but two others were abandonned due to hole collapse issues. These abandonned wells were in very promising production areas as per the reservoir model and due to the shallowenest of the reservoir, it was not possible to move the surface location. Therefore, the issues in the surface section needed to be solved in order to maximize profits in the country. Following a rigerous study for determining which is the optimal solution for drilling the surface section in this area of the field, Casing While Drilling (CwD) technology was selected and implemented in August 2019 in well A-1530D, next to the previous abandoned wells. CwD operation was performed with excellent results by drilling from 101ft to 520ft with no issues. CwD successfully isolated the higly problematic zones in the surface section and more importantly, allowed to reach areas of the reservoir that had high potential for production.

Advanced Light Weight Thixotropic Lost Circulation Cement Solution for Vugular and Natural Fractured Limestone Formations: UAE Offshore Case History

Lost circulation while drilling across vugular or naturally fractured limestone formations is a costly challenge and has financial impacts including nonproductive time and remedial operational expenses. Many fields in the UAE are encountering notorious lost circulation complications, which are difficult to control with conventional lost circulation solutions while drilling surface sections. Novel lightweight thixotropic cement has proven beneficial to take control of severe losses in these vugular and naturally fractured limestone formations. The main challenge while drilling across the surface section in UAE offshore field is the heavy or total loss of returns. Drilling performance is affected due to poor hole cleaning, a risk of stuck pipe, surface fluid handling problems, and well control risks. Conventional extended cement slurries have been widely used to cure losses while drilling but with limited success. A new lost circulation solution combines lightweight (10.5- lbm/galUS) high solids fraction cement (trimodal system) and a thixotropic agent, which develop fast gels with high compressive strength. Thus, it enables plugging of large voids and fractures to deliver the wellbore integrity required to continue drilling with enhanced performance and efficiency. Intensive laboratory qualification tests focusing on static gel strength and compressive strength development was performed to tailor the new solution. The results were promising with more than 100 lbf/100 ft2 of static gel strength in 10 minutes and compressive strength development of 1,000 psi within 24 hours at low surface temperature. In addition, a transition time (TT) on-off-on test demonstrated more rapid gel strength development when the shear is reduced and regained fluidity with reapplication of shear. In one of the wells, heavy losses were encountered while drilling across surface section. The lightweight thixotropic solution was pumped for the first time worldwide and it was shown that the innovative lost circulation solution was effective in significantly reducing the losses and enabled the operator to continue drilling to section TD. This case study demonstrates that this advanced system is effective in curing losses and reducing nonproductive time. The unique properties of faster rapid gel strength and high compressive strength make this solution effective for treating a wide range of lost circulation events while drilling. Furthermore, the advanced lightweight thixotropic cement lost circulation solution exhibits strong performance in curing heavy losses and establishing well integrity with reliability.

Casing While Drilling Level 2 as Mitigation for Shallow Gas and Loss Circulation Hazards in Surface Section

Casing while drilling Level 2 was introduced to mitigate problems in the surface section of Mutiara and Pamaguan Field in East Kalimantan. These two fields have historical shallow gas and loss circulation hazards in surface section. Following a blowout incident in Pamaguan in 2012, new policy was introduced for drilling the surface section in Mutiara and Pamaguan. A pilot hole must be drilled, and additional surface casing shall be set. Although considered safe, longer drilling days and vulnerability to repeated loss circulation made this method inefficient. A new approach to mitigate the problem was proposed by introducing casing while drilling Level 2 in 2020 drilling campaign. Many papers already discussed about the effectiveness of casing while drilling to mitigate loss circulation. However, a limited number of papers discuss casing while drilling to mitigate shallow gas. Costeno et al, 2012, discussed the use of casing while drilling to mitigate shallow gas. However, the risk of shallow gas was low and there was no shallow gas record during the execution. This paper specifically discusses about utilizing casing while drilling (CWD) technology to mitigate not only loss circulation, but also shallow gas risks during surface hole interval. Both hazards occurred in several wells during job execution and CWD with its plastering effect has managed to drill troublesome surface hole safely, thus making it the better alternative to achieve efficient drilling in comparison with the previously used pilot hole method.

Engineered High-Performance Lightweight Thixotropic Lost Circulation Solution for Vugular and Natural Fractured Formations UAE Case History

Lost circulation while drilling across vugular or naturally fractured formations is a difficult challenge which will come with high cost for the oil and gas industry. When lost circulation encounter, the drilling company will result in nonproductive time and remedial operational expenses. Most of the fields in UAE are encountering lost circulation problems while drilling across surface sections, which are difficult to control with conventional lost circulation solutions. Newly engineered high-performance lightweight thixotropic proves beneficial to control losses in vugular and natural fractured formations. The main challenge while drilling the surface section in one UAE field is the total loss of returns and flowing formation. This leads to the inability to continue drilling due logistics to continue producing drilling fluid and to keep the well under control and risk of stuck pipe due to poor cuttings removal. Conventional low-density cement slurries have been widely used to cure losses while drilling, but with low effectiveness. A new lost circulation solution that combines lightweight (10.5–lbm/galUS) high-performance cement and a thixotropic agent produce an engineered high-performance lightweight thixotropic lost circulation solution with fast gel strength and improved compressive strength, enabling the plugging of large voids and fractures to recovery wellbore integrity required to continue drilling. Extensive laboratory qualification tests were performed for static gel strength development to confirm the plugging efficiency and compressive strength development. The results were promising with more than 110 lbf/100 ft2 of static gel strength in 10 minutes and compressive strength development of 1,000 psi within 24 hours at low surface temperature. In addition, a transition time (TT) with on-off-on test demonstrated more faster gel strength development was developed when the reduction of the shear rate and regained pumpable with reapplication of shear. In one of the wells, total losses were encountered while drilling across surface section. The lightweight high-performance thixotropic solution was pumped for the first time worldwide, proved that the innovative lost circulation solution was effective in curing the losses, and enabled the operator to continue drilling the section to TD. This case study demonstrates that the engineered system is effective in curing losses and reducing nonproductive time. The unique properties of more faster gel strength and enhanced compressive strength make this system more effective for treating a different types of lost circulation scenarios during drilling (Jadhav and Patil, 2018). New high-performance lightweight thixotropic cement lost circulation solution exhibits strong performance in curing total losses and establishing well integrity with reliability.

Investigation of the Development of Localized Disturbances in the Boundary Layer of a Flat Plate under Conditions of Moderate Degree of the Incoming Flow Turbulence behind the Surface Step

In a wind tunnel on a flat plate in a separated flow behind a rectangular step, the emergence and development of localized disturbances generated by low-frequency impulse deviations of the local surface section under conditions of low and moderate degrees of the incoming flow turbulence is studied. The results were obtained by hot-wire anemometry at low subsonic flow velocity. It was found that impulse deviations of the wall generate disturbances, which are socalled Streaky structures and wave packets of oscillations. The separation of the laminar boundary layer accelerates the growth of wave packets with subsequent turbulization of the near-wall flow. The specific features of the behavior of localized disturbances under conditions of moderate degree of free-stream turbulence are revealed.

ANALYSIS AND IMPROVEMENT OF SEISMIC EXPLORATION METHODS IN EASTERN SIBERIA

Many enterprises and authors have often addressed the problem of increasing the efficiency of seismic exploration (geological constructions and forecasting) at the prospecting stage in the Siberian Platform (SP) throughout the entire period of oil prospecting in Eastern Siberia. This is confirmed by numerous publications and production reports. Unfortunately, it should be admitted that there is still no cardinal progress in solving this problem. The reasons for the low information content of geophysical materials for the SP conditions in these publications are substantiated and set out in great detail. This is both a sharply dissected relief, and small-block models of the near-surface section, and an energy dissipation in rudaceous pyroclastic rocks of the Triassic, background of reverberation, near-surface waves formed by thin layers of traps in near-surface section, local velocity anomalies in the middle part of the section, background and interference of partially multiple reflections, complex salt tectonics, blocking and tesselation of secondary changes in Riphean rocks, forming tesselation of seismoacoustic properties. These are the main, in authors’ opinion, reasons reducing reliability of the geological section forecast based on seismic data. Some of them are removed using a complex of geophysical data. But tie, backbone on seismic horizons lies also at the heart of integration. Therefore, increasing the information content of seismic survey in regard to fixing the reflecting boundaries based on selection and substantiation, field observation systems and technologies is the most important issue in the problem under discussion.

Stratigraphic Analysis of Gercus Formation in Dohuk area, Northern Iraq

A surface section of the Gercus Formation (Middle-Late Eocene) was studied in Berafat area, Dohuk Governorate, Northern Iraq. The Gercus Formation consists of a mixed siliciclastic sediments, evaporates and carbonate sequences in the studied region, predominantly in the upper and middle parts. Nevertheless, it usually consists of upward-fining carbonate-rich sandstone cyclothems, marl, conglomerate and siltstone along with a gypsum lens and thin micrite carbonate beds. The Gercus Formation was deposited in delta and delta front of occasionally depositional environment which is represented by red-brown claystone and reddish-brown mudstone lithofacies. Cross bedded pebbly sandstone, trough cross-bedded sandstone and laminated cross-bedded sandstone lithofacies are deposited in braided delta environment. Marl lithofacies and gypsum lithofacies are deposited in intertidal and supratidal environments. The sea level fluctuation caused the river base level to occasionally rise and fall. In addition, the process changed from erosion to deposition, while the grain size also changed at different environments from gravel to sand and clays. The Gercus succession of northern Iraq was developed during the Middle-Late Eocene in an active margin basin, where the last stage closure of the New-Tethys and its collision with the Eurasian plate took place between the northeastern Arabian plate. It caused major episodes of uplifts and subsidence along with base level variations due to eustatic ups and downs. Within Gercus Formation, several fourth order cycles can be recognized, reflecting generally asymmetrical cycles, as well as the difference between sediment supply and accommodation space.

Primaries Oblateness Effects on the Collinear Libration Points in the Restricted-three Body Problem

In this work, the canonical Hamiltonian form of the restricted three- body problem including the effects of primaries oblateness is presented. Moreover, the collinear libration points are obtained. In addition to this, the relation between position of libration points and variation in (mass ration , oblateness coefficients A1 and A2) is studied. The results obtained are a good agreement with Perdios [1] & Singh [2]. The Poincare surface section PSS is used to illustrate the stability of motion around each of the collinear libration points. A numerical application on the real system Earth-Moon is presented.

Generation of disturbances in the boundary layer of a flat plate by periodic low-frequency motion of the surface section

The development of localized disturbances, generated by periodic impulse lifting of three-dimensional surface in the flat plate boundary layer at Reδ1 > 400 is experimentally investigated. It is shown that a large amplitude surface lifting leads simultaneously to the formation of two types of perturbations in the boundary layer: longitudinal localized structures and two wave packets. Spatial development of oscillations at the central frequency of the wave packets is consistent with the linear theory of hydrodynamic stability.