Deepwater Wells Research Articles

Status and Prospects of Dual-Gradient Drilling Technologies in Deep-Water Wells

Status and Prospects of Dual-Gradient Drilling Technologies in Deep-Water Wells

Coupling effect of annular volume change and non-linear fluid thermal property on annular pressure buildup in multi-layer annuluses of deepwater well

Coupling effect of annular volume change and non-linear fluid thermal property on annular pressure buildup in multi-layer annuluses of deepwater well

Computationally efficient simulation of non-isothermal two-phase flow during well construction using a new reduced drift-flux model

• A novel reduced drift-flux model for non-isothermal two-phase flow is developed. • This model considers transient heat transfer and gas-in-oil solubility behavior. • This model shows higher accuracy compared to historical reduced drift-flux models. • This model runs two orders of magnitude faster than real-time. • This model is validated using both field data and benchmark models. Two-phase flow modeling is important in well construction field for well planning and real-time applications. In this paper, a new non-isothermal two-phase flow model is presented that improves upon the simulation accuracy and capability of historical reduced drift-flux models (RDFM) while still retaining high computational efficiency. Built on the “no pressure wave” assumption of the RDFM, our new RDFM achieves improvements through calculating the temperature dynamics, considering interface mass transfer (i.e., gas-in-oil solubility behavior), and introducing a new lumped pressure dynamics model. By including these physical factors that are critical for practical applications, the proposed RDFM shows higher simulation accuracy and capability compared to historical RDFMs. The validity of the proposed model is proven by comparing it to field measurements, benchmark models, and the classical drift-flux model. Moreover, the proposed RDFM successfully retains the high computational efficiency of historical RDFMs even with the addition of the aforementioned complex physical dynamics. When conducting full-scale gas influx simulations, the proposed RDFM achieves a computational speed at more than two orders of magnitude faster than real-time. Due to its good performance on both computational efficiency and simulation accuracy, the proposed model is suitable for real-time applications in most well construction scenarios. It is especially superior to historical RDFMs when simulating more complicated but still common scenarios, e.g., deepwater wells drilled in high-pressure high-temperature environments, and wells experiencing gas-in-oil solubility behavior.

Comprehensive workflow to quantify diagenetic cement from wireline logs of deep water east coast of India wells and rock physics modeling

Presence of diagenetic cement is common in deep-water siliciclastic reservoirs and largely affects reservoir quality. Hence, the quantification of cement volume is an integral part of the reservoir characterization workflow. Lab analysis of core samples provides the cement volume information used as input for rock physics modeling. In the absence of core sample analysis, use of analogous offset well information provides an approximate estimate of cement. In reality, most deep-water wells do not have core samples for lab analysis. Consequently, the availability of offset well information is sparse and sometimes unavailable. Hence, getting an accurate cement volume estimate for reservoir characterization is challenging. For a detailed analysis, it is desirable to have a continuous measurement of cement volume across the reservoir sand. Presence of a calibrated cement volume log for the entire reservoir improves rock physics modeling. In this work, petrophysical M-N lithology cross plot, which is widely used to identify lithologies, has been used to quantify the diagenetic cement present within the reservoir, where M is the density normalized sonic values and N is the density normalized neutron values. Here, the M and N has been used as M-Lithology (MLITH) and N-Lithology (NLITH). In estimating MLITH and NLITH values, compressional sonic, bulk density and neutron logs are used. Porosity estimated from neutron/density is useful to identify the type of cement. Whereas, sonic slowness values are more sensitive towards the amount of grain contact cements. Hence, the estimated values of MLITH and NLITH varies differently in the presence of diagenetic materials. These variations of MLITH and NLITH values are captured and converted to cement volume fractions. In the presence of core data, the lab analysis measurements are used to calibrate the cement volume log. Further, rock physics modeling results helps to validate the output. The results of the study add value by quantifying diagenetic cementation in the reservoir characterization process by mitigating the associated limitations due to absence of sufficient core data.

A Prediction Model of Pressure Loss of Cement Slurry in Deep-Water HTHP Directional Wells

The exploitations of deep-water wells often use directional well drilling to reach the target layer. Affected by special environments in deep water, the prediction of pressure loss of cement slurry is particularly important. This paper presents a prediction model of pressure loss suitable for deep-water directional wells. This model takes the complex interaction between the temperature, pressure and hydration kinetics of cement slurry into account. Based on the initial and boundary conditions, the finite difference method is used to discretize and calculate the model to ensure the stability and convergence of the result calculated by this model. Finally, the calculation equation of the model is used to predict the transient temperature and pressure loss of Wells X1 and X2, and a comparison is made between the predicted value and the monitoring data. The comparison results show that the maximum error between the temperature and pressure predicted by the model and the field measured value is within 6%. Thus, this model is of high accuracy and can meet the needs of site construction. It is concluded that this result can provide reliable theoretical guidance for temperature and pressure prediction, as well as the anti-channeling design of HTHP directional wells.

Study on annular pressure buildup phenomenon in subsea wells considering the effect of cement

AbstractIn marine fossil energy production, annular pressure buildup (APB) caused by temperature increase is a widely concerned problem and needs to be solved urgently in subsea wells. To study and predict APB and avoid consequent safety accidents and economic losses, a novel model is proposed to predict APB considering the effect of cement. The model has a wider application range by considering the dynamic change of thermal properties and mass change of the annular fluid. Laboratory experiments were conducted to verify the accuracy of the proposed model. Then a case study and mitigation evaluation were conducted to make the further analysis. Research results show that cement has a significant effect on APB, ignoring the cement may bring potential danger. The height of cement affects APB differently when the top of cement (TOC) is above and below the previous casing shoes. Making the TOC below the previous casing shoe could provide a leakage surface for annular fluid. It is an effective method for APB mitigation but a balance needs to be struck between wellbore integrity and mitigation effect. Gas or foam injection is another effective method to mitigate APB. The necessary gas volume varies with the annular pressure and initial gas pressure and needs to be determined according to the actual condition, especially in deepwater wells.

Alteration of Fractured Foamed Cement Exposed to CO2-Saturated Water: Implications for Well Integrity

Geologic CO2 storage (GCS) is a method to mitigate the adverse impact of global climate change. Potential leakage of CO2 from fractured cement at the wellbore poses a risk to the feasibility of GCS. Foamed cement is widely applied in deepwater wells where fragile geologic formations cannot support the weight of conventional cement. Thus, it is critical to know whether fractures in foamed cement self-seal in a similar manner as conventional cement systems. This study is the first to investigate the changes in physical and chemical attributes of foamed cement under dynamic flow conditions using CO2-saturated water. Self-sealing of fractures in the cement was observed at a solution flow rate of 0.1 mL/min and a pressure of 6.9 MPa. The formation of CaCO3 precipitates in pore spaces and fractures led to a decrease in permeability by 1 order of magnitude. The extents of self-sealing in foamed cement samples, specifically the 20 and 30% air volume formulations, were similar to that of conventional cements. We attribute this to the greater alteration depth in the foamed cement, which compensated for the reduced availability of Portlandite and higher initial porosity. The results can be used to evaluate the risk of leakage associated with foamed cement.

A Novel Method for Fracture Pressure Prediction in Shallow Formation During Deep-Water Drilling

Abstract Large numbers of deep-water drilling practices have shown that more than 60% of deep-water wells have complex leak-off during the drilling process, which poses great difficulties and challenges for the safety and operation time of deep-water drilling. The purpose of this article is to establish a method for predicting the fracture pressure in shallow formations. In this study, the deep-water shallow formation was divided into the upper unconsolidated soil layer, and the lower diagenetic rock layer according to the geotechnical distribution characteristics of the deep-water shallow formation. The location of the transition soil/rock layer zone was determined using the upper soil layer density trend line, and the lower rock layer density log data regression trend line. The deep-water shallow fracture pressure prediction model was established based on the soil/rock transition zone. The shear failure criterion was used above the transition zone, and the tensile failure criterion is used below the transition zone. The shallow fracture pressure of six drilled exploratory wells in the X block from the South China Sea was calculated using this new method and the calculation errors were all less than 3.18%. Moreover, the shallow fracture pressure body in this block was established using the Kriging interpolation method based on six drilled exploratory wells data. This shallow fracture pressure body established here was used to predict nine development wells shallow fracture pressure with a predictive error of less than 1.7% and there were no drilling accidents. The case study demonstrates that the new model can significantly improve the prediction accuracy has good prospects for popularization and application.

Analysis of hydrocarbon under-filled and water-filled Miocene deepwater reservoirs, eastern Mexico offshore

Hydrocarbon exploration in the deepwater portion of the southwestern Gulf of Mexico commenced a decade ago, but discoveries have not been able to meet the optimistic expectations based on historical success in the northern Gulf of Mexico. Despite the existence of organic-rich source rocks and high-quality Miocene reservoir rocks, there is a concern that the lack of significant hydrocarbon accumulations in some prominent traps in the northern Catemaco fold belt (Veracruz Trough) resulted from an ineffective sealing and/or trapping mechanism.By integrating drill core, 3D seismic, and well data provided by the Mexican National Hydrocarbon Commission (CNH), this paper attempts to evaluate the cause of hydrocarbon under-filled or water-filled Miocene traps within the Veracruz Trough, using the prominent structural closures drilled by Pemex-operated Kunah-1 and Yoka-1 deepwater wells as case studies. Three hypotheses are considered and analyzed for these two large traps: top seal leakage, existence of unmapped shallow spill points, and late trap formation relative to timing of hydrocarbon generation and migration.Seal rock leakage analyses, which involves downhole pressure data analysis and mercury injection capillary pressure laboratory measurements on cuttings, suggest that many of the evaluated intra reservoir and top seal rocks could have held significantly taller hydrocarbon columns than encountered by the wells. In addition, 3D seismic structural interpretation around the Yoka trap indicates that all mapped spill points are much deeper than the observed fluid contacts. However, the trap formation timing assessment shows that by the time the traps began to develop, the main oil generation phases had largely concluded, and gas generation was at a very late stage for the most prominent source rocks. Consequently, a more robust explanation for the Kunah and Yoka under-filled and water-filled structures is due to a timing mismatch, with late trap formation relative to an earlier hydrocarbon charge.

A graph model analysis of the conflict in the irrigated perimeter in Chapada do Apodi-Brazil

A conflict situation arises whenever there is a dispute between two or more individuals or groups of individuals with different decision-making powers and interests. In this context, this research aims at analyzing the application of the Graph Model for Conflict Resolution (GMCR) in disputes over the use of water resources in the irrigated perimeter located in Chapada do Apodi/CE, Brazil. Chapada do Apodi has great economic development potential for the State of Ceará in Brazil since there is high quality soil for agricultural practice. This potential made it possible to implement a public irrigation perimeter in this region. The water supply has become decisive for the full development of the region and, due to the low water supply, conflicts between small, medium and large producers have intensified. In this paper, we provide some insight into this conflict through a stability analysis using the GMCR. The stability analysis points out as a conflict resolution a scenario representing the situation where governmental organizations require the implementation of a water reuse system by large companies and do not increase the water pumping tariff for producers, small farmers drill deep water wells, agribusiness does not grow crops that consume less water, and civil society offers political training and social mobilization in support of small farmers. In particular, the stability analysis carried out suggested as a conflict resolution a scenario which comprises both water consumption reduction from small and large farmers and also political training and social mobilization of the small farmers.

Study of dynamic pressure on the packer for deep-water perforation

Abstract The packer is one of the most important tools in deep-water perforation combined well testing, and its safety directly determines the success of perforation test operations. The study of dynamic perforating pressure on the packer is one of the key technical problems in the production of deep-water wells. However, there are few studies on the safety of packers with shock loads. In this article, the three-dimensional finite element models of downhole perforation have been established, and a series of numerical simulations are carried out by using orthogonal design. The relationship between the perforating peak pressure on the packer with the factors such as perforating charge quantity, wellbore pressure, perforating explosion volume, formation pressure, and elastic modulus is established. Meanwhile, the database is established based on the results of numerical simulation, and the calculation model of peak pressure on the packer during perforating is obtained by considering the reflection and transmission of shock waves on the packer. The results of this study have been applied in the field case of deep-water well, and the safety optimization program for deep-water downhole perforation safety has been put forward. This study provides important theoretical guidance for the safety of the packer during deep-water perforating.

West Africa Salt-Zone Cementing Best Practices: Laboratory Evaluation and 5-Year Field Application Review

Summary To determine which salt-based cement system (potassium chloride or sodium chloride) was suitable for cementing across halite and anhydrite salt sections in West Africa, eight slurry recipes were tested to assess how formation salt contamination would affect slurry properties. The formation salt used for testing was sampled from a deepwater, presalt well in Angola. The recommendations developed from the laboratory study were implemented in 10 projects across West Africa over 5 years with 100% operational and well integrity success. A candidate deepwater well was selected in which the surface and intermediate strings penetrated salt formations. Four slurry designs (a lead and tail slurry used on each casing string) were programmed. Each slurry was designed and tested as two distinct systems using potassium chloride and sodium chloride salt, respectively, yielding a total of eight slurry designs. Using the methodology and data presented by Martins et al. (2002), the mass of dissolved formation salt that each slurry may receive during placement was estimated and duly incorporated into each slurry design. Subsequently, the salt-contaminated slurries were tested and compared with the properties of the initial uncontaminated slurries. On the basis of these results, conclusions were then made on which salt slurry system (potassium chloride or sodium chloride) exhibited better liquid and set properties after contamination with formation salt. Subsequently, this knowledge was applied to 10 projects across three countries in West Africa. This study showed that when the contact time of liquid cement slurry to salt formation was low—typically when the salt-formation interval across which the cement slurry flowed was less than 100 m thick—the level of formation salt dissolution entering the slurry during placement was limited. In this case, a potassium chloride salt-based slurry delivered improved liquid and set properties as compared with a sodium chloride salt-based slurry. In the field, this knowledge was applied in all oilfield projects cemented by an oilfield service company between 2015 and 2020. This included deepwater, shallow offshore, and onshore wells. All related salt-zone cement jobs, including sidetrack plugs, placed across the salt formations were successful on the first attempt. In an absence of industry consensus around salt-formation cement slurry design, this paper validates a guideline for West Africa, based on results from laboratory testing and 5 years of field application. In contrast to current literature that recommends only sodium chloride salt-based slurry designs across halite or anhydrite salt intervals, this work demonstrates that potassium chloride salt-based slurry systems can effectively be used to achieve well integrity where a halite or anhydrite salt interval is less than 100 m (328.1 ft) thick.

Occurrence of carcinogenic illudane glycosides in drinking water wells

BackgroundPtaquiloside (PTA), caudatoside (CAU) and ptesculentoside (PTE) are carcinogenic illudane glycosides found in bracken ferns (Pteridium spp.) world-wide. The environmentally mobile PTA entails both acute and chronic toxicity. A comparable risk might be associated with the structurally similar CAU and PTE. It is of great health concern if these compounds are present in drinking water, however, it is currently unknown if these compounds can detected in wells in bracken-dominated regions. This study investigates the presence of PTA, CAU, PTE, and their corresponding hydrolysis products pterosins B (PtB), A (PtA) and G (PtG) in water wells in Denmark, Sweden and Spain. Water samples from a total of 77 deep groundwater wells (40–100 m) and shallow water wells (8–40 m) were collected and preserved in the field, pre-concentrated in the laboratory and analysed by liquid chromatography–mass spectrometry (LC–MS).ResultsDeep groundwater wells contained neither illudane glycosides nor their pterosins. However, seven private shallow wells contained at least one of the illudane glycosides and/or pterosins at concentrations up to 0.27 µg L−1 (PTA), 0.75 µg L−1 (CAU), 0.05 µg L−1 (PtB), 0.03 µg L−1 (PtA) and 0.28 µg L−1 (PtG). This is the first finding of illudane glycosides and pterosins in drinking water wells.ConclusionsDetected concentrations of illudane glycosides in some of investigated wells exceeded the suggested maximum tolerable concentrations of PTA, although they were used for drinking water purpose. Contaminated wells were shallow with neutral pH and lower electric conductivity compared to deep groundwater wells with no illudane glycosides nor pterosins.

Prediction of the wellhead uplift caused by HT–HP oil and gas production in deep-water wells

In the oil and gas production process in deep-water high-temperature–high-pressure (HT–HP) wells, the occurrence of wellhead uplift is often induced by the heat carried by oil and gas flow from the well bottom to the wellhead. This directly leads to the seal failure of wellhead device, causing the great potential safety hazard. Therefore, the wellhead uplift needs to be studied in cementing designing. The calculation model for the wellbore temperature and pressure field as well as the wellhead uplift height was established, we have developed a wellhead uplift experimental device, and experiments for the wellhead uplift under different working conditions were conducted. It was found that the increase of wellbore temperature and trap pressure cause the wellhead uplift, the calculation error of model is less than 10% compared with the experimental data. This could be used to predict the wellhead uplift height under different working conditions. It has certain guiding significance for cementing optimization and improvement of the wellhead integrity.

Analysis of water supply sources in Kormilov district of Omsk region

The article describes the sources of water supply inKormilovka district of Omsk region. The main sources of water are surface waters of the Om and Taburga rivers, lakes and artificial reservoirs, groundwater. In general, the territory of Kormilovka district lacks fresh groundwater. Currently, water is supplied by hydraulic structures on the Omriver as part of water intake and treatment facilities, water pipelines and a pressure distribution network. Water supply from underground sources is carried out from tubular wells with a depth of 5.0 - 9.0 m, from wells with a depth of 200 m and deep-water wells of about 1100 m. Water intakes from underground sources are available in almost all rural settlements, but they are used for technical and (or) economic purposes. An ecological assessment of the state of surface and underground sources isprovided. The results of an analysis of the geological and hydrogeological situation are presented. Of greatest interest are Neogene-Quaternary, Upper Oligocene-Lower Miocene and Lower Upper Cretaceous (Pokursky) complexes. According to the generalized characteristics of quality of groundwater from three underground aquifers in Kormilovka district, the most acceptable is the Pokursky aquifer, since itsgroundwaters are less mineralized, softer, more protected, and, consequently, their microbiological and parasitic indicators comply with the sanitary standards. When using both surface and groundwater for household and drinking purposes, it is environmentally safe for the population only after adjusting such indicators as turbidity, color, chlorine, iron, and dry residue content and bringing the microbiological indicators to SanPiN 2.1.4.1074-01 and SanPiN 2.1.4.544-96.

Use of the Hydraulic Model for the Operational Analysis of the Water Supply Network: A Case Study

This paper presents an analysis of the operation of the water supply system. The analysed network provides water to six small towns. The water supply network covers rural areas of approximately 50 square kilometres with a total of 6130 inhabitants (2020). The area is characterised by relatively large differences in elevation. The water-pipe network supplies water mostly to family housing, public utility buildings, recreational buildings, service and craft entities, religious buildings, and commercial facilities and farms, including breeding farms. The network is supplied from one deep water well and a centrally located water supply tank. A hydraulic model was used for the analysis. The model was developed using the Epanet program, based on numerical and operational data. After validation, selected measurement points were used to calibrate the model. Furthermore, a series of simulations were performed to illustrate the network operation for variable water supply and demand conditions. Single-period analysis was used for modelling due to the type of data obtained. The model allowed for the determination of the head of pressure in the network points and flows in particular sections for the operation parameters studied. The analysis showed that at present, the network is not operating stably. In the case of average demand, water is supplied to all users, but there are areas in the network characterised by high pressure. On the other hand, during maximum water demand, due to the limited water supply to the water reservoir, from which most of the network is supplied, there are water deficiencies that cannot be compensated for by the operating pumping system.

Prediction of Hydrate Formation Risk Based on Temperature–Pressure Field Coupling in the Deepwater Gas Well Cleanup Process

Deepwater oil and gas exploitation has become an important field in the petroleum industry development. However, there are still no mature methods for hydrate prevention in the deepwater wells clea...

Application of innovative lost circulation cement spacer for production casing in deepwater wells.

Application of innovative lost circulation cement spacer for production casing in deepwater wells.

Multilevel Completions in One Trip: Development and Deployment

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 30747, “Tripping the Light Fantastic: When Three Become One,” by Euan Murdoch, SPE, Paul Day, and Steven Walduck, Weatherford, prepared for the 2020 Offshore Technology Conference, originally scheduled to be held in Houston, 4-7 May. The paper has not been peer reviewed. Copyright 2020 Offshore Technology Conference. Reproduced by permission. Typically, the completion of certain deepwater wells will necessitate the separate deployment of sandface, intermediate, and upper completions. What if this could be achieved in a single trip? In the simplest terms, completing in a single trip reduces the overall completion time by half and more. The complete paper describes the hurdles that have prevented single-trip installation of upper and lower completions in the complex world of subsea and deepwater applications and examines the processes, technologies, and risk-mitigation steps that took a concept from pilot to successful deployment. Introduction Almost universally in offshore operations, operators have elected to deploy completions in multiple trips. Simple completions on land are often deployed in a single-trip fashion, and the deployment of cemented single-trip gas-lift systems on platform locations in the Gulf of Thailand is commonplace. Subsea single-trip systems have been deployed in the Campos Basin; however, these tend to be relatively simple and in wells not requiring sand-control solutions. They typically consist of a safety valve, gas-lift mandrels, polished bore receptacle (PBR), production packer, and re-entry guide. At the time of writing, no one has run standalone screens as a single-trip system in deepwater applications.

Quantitative analysis of slope stability of drilling sites with complex topography in the Qiongdongnan continental slope

Due to the large slope angle and the weak strength of submarine soils, Qiongdongnan deepwater continental slopes face great instability problems. In continental slope area, evaluating the stability of the slope before drilling is important as slope instability threatens the drilling safety. Taking the Lingshui deepwater well site as an example, 2D and 3D submarine slope stability calculation models, which consider the vertical heterogeneity of soil strength, were established based on the strength reduction method and Flac3D. The vertical profile of the soil shear strength was obtained via cone penetration and geotechnical tests. The effect of returned cuttings and drilling disturbance on slope stability were analyzed, and the safety factor of the slope was calculated. In addition, the position of potential slip surfaces and the possible slip directions were analyzed. Based on this, the location of the well was determined. The results indicate that the minimum safety factor of slope, which crosses the well, is 1.32. Moreover, the risk of submarine landslide is low. One potential landslide mass exists. However, the slope near the well is stable, and the slip direction of the landslide mass does not point to the well. The returned cuttings from the borehole decrease the safety factor and increase the risk of slope instability near the well.