bluuebunny/crossref_metadata_2025 huggingface dataset:
Mini DST to Characterise Formation Deliverability in Unconventional Reservoirs
Authors: Kurtoglu B. , Kazemi H. , Boratko E.C. , Tucker J. , Daniels R.
Published: March 2015

Characterization of reservoir deliverability is fundamental for the economic development of any field. In the Bakken, a need exists for reliable pressure transient tests to provide effective formation permeability of the combined fracture-matrix porous formation. This effective permeability can then be compared to laboratory measured core permeability of the matrix rock samples. This comparison is the basis for planning early production options and subsequent decisions for EOR alternatives. In the Bakken this understanding is particularly important because of the influence of massive hydraulic fracture stimulation on reservoir performance.

Determining well deliverability potential by conventional drill stem tests (DST) or traditional wireline formation tests (WFT) in the past has resulted in mixed success in the Bakken. On the other hand, the mini-DST has definitely increased reliability and the success rate of pressure transient tests. The operation of mini-DST tool requires much less time than the classic DST, and multiple zone tests can be conducted to assess individual zone deliverability. The Mini-DST tool uses the conventional Wireline Formation Tester (WFT) configured with a dual-packer module and downhole pump. Tests are conducted by inflating the dual-packer module to isolate a 3-foot interval of the wellbore. Then, formation fluid is pumped out from the packer-isolated wellbore interval followed by a pressure buildup in the interval. Some simple overlay comparisons, as well as conventional pressure transient analysis, are used to interpret the drawdown and buildup pressure responses.

In this paper we present several field tests which were analyzed both by conventional pressure transient analysis and numerical simulation. The analyses have provided insight into a better understanding of the flow mechanism in the Bakken both during primary production and in forecasting various improved and enhanced oil recovery proposals. The experience can also serve as a basis for test design in similar low-permeability reservoirs.
Study of Progressive Flow Profile of Multiphase (Oil-Water-Gas) Flow for Downhole Monitoring Applications
Authors: Rawool Amitkumar , Pawar Bharat , Naik Harit
Published: March 2015

Computational fluid dynamics (CFD) has been actively used to make flow profile predictions in down hole oil and gas environments. The flow in oil wells inherently consists of oil, water, and gas phases. Flow profile predictions are complicated by parameters such as fluid properties, flow velocities, area, and well inclination. A proper understanding of flow behavior under various operating conditions is critical when designing down hole equipment and flowmetering applications.

This paper presents case studies involving the three-phase flow of oil-water-gas in a down hole tubular. Phase distribution is analyzed for different compositions by varying the individual phase volume fractions. Various flow regimes, such as stratified flow, homogeneous flow, and bubbly flow, are studied individually as well as in their transition from one regime to another. The transition criteria were also studied. Extensive efforts were focused on understanding random bubble distribution, bubble breakup, bubble-relative movement, distortion, and diffusion in fluid flow with respect to flow variables. Finite volume phase distribution for oil vs. water is obtained as a function of time and distance (coherence) for multiphase flow in production tubulars. The effect of geometry changes with the objective of flow homogenization is also studied to enable the locations and numbers of monitoring devices to be fixed. CFD results were found to be comparable to single-phase analytical solutions. The examples and references included in the paper demonstrate the accuracy of the study results.

The studies verify that an understanding of flow dynamics is essential to evaluate optimum configurations of the variables described. Advanced knowledge of flow characteristics enables engineers to deliver robust and maintenance-free sensing technology for use in a subterranean environment.
New Stimulation Technologies in a Major Gas Field in the Middle East
Authors: Al-Ghazal Mohammed , Al-Driweesh Saad , Al-Sagr Abdulaziz , Al-Ghurairi Fadel
Published: March 2015

In their natural state, most gas wells in the Middle East do not produce at their optimum level. This is mainly attributable to formation tightness or near-wellbore damage caused by drilling operations; however, a properly designed and executed stimulation program can enable more commercial gas production rates at higher flowing wellhead pressures (FWHPs). For this reason, and others, stimulation jobs (e.g., hydraulic fracturing and matrix acidizing) are common completion operations in the Middle East.

In recent years, stimulation technologies have witnessed major advances, as their use has been the main driver for production from tight reservoirs worldwide. This paper outlines eight new stimulation technologies that have been recently deployed in a major gas field in the Middle East. In addition, the paper looks at candidate selection, the main characteristics and benefits of the technologies, and post-treatment results.

Overall, the production results from the use of these technologies have been very positive and impressive, and the forecast is that their implementation will grow considerably over the coming years. The value of these new technologies will become even more significant as our industry accelerates the development of unconventional resources.
A New Method for OBM Decontamination in Downhole Fluid Analysis
Authors: Zuo Julian Y. , Creek Jefferson , Mullins Oliver C. , Chen Li , Zhang Dan , Jia Na
Published: March 2015

Downhole fluid analysis (DFA) has been used successfully to delineate reservoir vertical and lateral connectivity and properties of the produced fluids. The DFA tools can measure bulk fluid properties such as gas/oil ratio (GOR), light-end compositions (CO2, C1, C2, C3-C5 and C6+), oil-based mud (OBM) filtrate contamination level, color (optical density) that is linearly related to the heavy ends (asphaltenes and/or resins), live fluid density and viscosity, etc. in real time at downhole conditions.

Because of overbalance of drilling and formation pressures, and miscibility of OBM filtrate with formation hydrocarbons, the sampled hydrocarbon fluid is usually contaminated by OBM filtrate. This OBM filtrate contamination affects an accurate characterization of the reservoir fluid. On the other hand, DFA flowline temperature is slightly different than formation temperature. DFA flowline pressure, however, may be significantly different from formation pressure because the flowline pressure can be below the formation pressure when the DFA sensor is beside the probe/packer or above the formation pressure when it is on the output side of the pumpout within the Wireline Formation Tester (WFT). Therefore, decontamination of OBM filtrate on fluid properties and conversion of them from flowline to formation conditions are of great importance to interpret DFA measurements.

A new reliable method has been developed in real time for characterizing downhole reservoir fluids, decontaminating OBM filtrate on the DFA-measured fluid properties and converting the DFA data from the flowline to formation conditions. The method has been validated against laboratory measurements of different types of reservoir fluids and OBM filtrates with successful results. This methodology establishes a powerful approach for conducting decontamination of OBM filtrate on DFA measurements in real time at downhole conditions.
Case Study: Successful Application of Coiled Tubing Conveyed Inflatable Straddle Packer for Selective Reservoir Treatments in Deviated and Horizontal Wells of Rajasthan Field, India
Authors: Singh Alok Kumar , Kothiyal Manish Dutt , Kumar Prakash , Sharma Anurag , Mahajan Mahesh
Published: March 2015

Field X in Rajasthan, India has been developed with 22 Injectors wells &40 Producers wells. Most of the producers are completed with standalone screens of different types like conventional, ICD's and SSD types. Almost 60% of the producers are completed with ICD type screens. The open hole for screens section has been drilled with 10.2 ppg SBDIF (Synthetic based drilling fluid)which includes dolomite and barite as weighting agents. After running the screens, the screen section is displaced with 8.4 ppg low weight SBDIF(Synthetic based Drill-In Fluid) which has organophilic clay (Viscosifier) and emulsifier as the key components. Due to some operational delay in bringing the wells online, mud was left inside the screens for a few months. The deposition of mud filter cake and heavier hydrocarbon probably choked the ICD screen sensuing a number of ICD's non-contributing. Conventional stimulation techniquesdidn't help in achieving good results.

To effectively remove the suspected damage a coiled tubing based solution was implemented which involved the application of Inflatable Straddle Packer tool. It provides pinpoint accuracy for conventional, horizontal and multilateral stimulation treatments. Coiled Tubing Conveyed Re-Settables elective straddle packer elements allow multiple settings in one trip. Treatment Valve allows precise injection of treatment fluid & adjustable element spacing helps in straddling the long interval.

A case history of successful application of CT conveyed inflatable straddleapcker tool in field X in India is presented in this paper which enabled the correct placement of a series of stimulating chemicals targeting different damage mechanisms i.e. wax deposition, mud filter cake, inorganic scaling etc. Post stimulation production logs showed excellent improvement of conformance in zonal contributions.

The learning from this stimulation technique was also applied to the horizontal wells in field Y with very encouraging results.
Nanostructured Material Based Completion Tools Enhance Well Productivity
Authors: Xu Zhiyue , Richard Bennett M. , Solfronk Matthew D.
Published: March 2015

Making downhole completion tools interventionless is the ultimate level of integrated design of material and product that enhances well performance and saves operation time and cost. Two common approaches to interventionless tools are novel mechanical design and use of new engineered materials. New interventionless tool designs, though effective, are often limited to the small downhole geometry available. Use of high strength, disintegrable materials becomes a more attractive solution for downhole tools which require eventual removal after the tool completes its functions. This paper presents a new, groundbreaking, smart, disintegrable nanostructured composite (DNC) and its successful use for multistage fracturing tools to enhance shale gas/oil well productivity.

The disintegrable nanostructured composite (DNC) is manufactured through a powder metallurgy process by consolidating reactive metal powders that were coated with metallic and/or ceramic reinforcements. Material composition and microstructure were engineered at the micro- or nanoscale, to vary material strength and disintegration rate. The DNC is lighter than aluminum and stronger than some mild steels, but disintegrates when it is exposed to the appropriate fluid. More broadly, the DNC has the potential for radically changing the downhole tool functionality landscape by reducing product operational complexity and potentially the wholesale elimination of complete well trips by causing all, or a portion of, a tool to disintegrate in the well.
Three-Dimensional Analysis on Stress Patterns within a Sub-salt Formation and an Integrated Method for the Design of a Mud-Weight Window
Authors: Shen Xinpu
Published: March 2015

Borehole stability and pore pressure environments downhole transition abruptly, often detrimentally in the presence of salt formations. Geomechanical regimes can vary considerably above, through, and below salts, making accurate modeling of them necessary but challenging. This paper proposes an integrated method that has been developed for predicting the Mud-Weight Window (MWW) of subsalt wells. The high efficiency of the 1D method and high accuracy of the 3Dmethod are deliberately combined in the proposed integrated method, while the disadvantages of those methods are avoided. This objective is achieved by calculating the effective stress ratios, which are part of the input data of the 1D method, with a 3D finite-element (FE) model. The effective stress ratio brings a 3D property into the 1D solution of MWW, thus giving it a 3Dproperty.

A 3D model, where the wellbore trajectory was accurately referenced, was built to illustrate and validate the proposed method. A salt body with a thickness of 5.8 km was included. The distribution of the effective stress ratio within the model has been calculated and used in the numerical prediction of the 1D MWW. The prediction of a 3D MWW corresponding to the wellbore trajectory is then derived in the subsalt formation and merged with the numerical prediction.
An Experimental Study on Mitigation of Oil Well Cement Gas Permeability
Authors: Ozyurtkan M. Hakan , Altun Gursat , Mihcakan I. Metin , Serpen Umran
Published: March 2015

Permeability development within and around the cement, placed in the casing-hole annulus in oil and gas wells, is a frequently encountered worldwide problem that might lead to various adverse economic and, possibly, catastrophic consequences. The resultant loss of hydrocarbon production and, sometimes, the wells constitutes the major part of the adverse economic impact. The loss of wells, in turn, might lead to severe environmental pollution and most importantly the loss of lives. Sustained casing pressure (SCP,) described as the pressure buildup due to flow through the permeable cement matrix or the micro annulus developed around the cement, had been experienced by about sixty percent of the wells producing oil and/or gas in the Gulf of Mexico, according to the literature. Although various methods are used to prevent the problem, there is no widely accepted universal method by the industry. Currently, the problem is attempted to be mitigated using distinct methods applied either during the cementing operations or after the problem is detected.

The present study is an experimental investigation for the prevention of permeability development within and around the set cement at ambient conditions. A natural magnesium complex with carbonate, coded ARI, is used the first time ever as a cement additive to achieve desired prevention. Gas permeability measurements are conducted on the samples of cements of 19 different compositions, at the end of the successive curing periods up to 28 days. ARI containing cement samples are found to develope an impermeable matrix to gas flow and to exhibit no shrinkage in volume during setting. The performance of ARI as a cement additive is also investigated in the presence of other commonly used cement additives, e.g. friction reducer and fluid loss controlling agents.
Comparative Study on Stress-dependent Permeability of Ultra-low Permeability Sandstone Rock Using Different Types of Fluid Media
Authors: Qi Teng , Junchang Sun , Zhengming Yang
Published: March 2015

During the production lifecycle of a reservoir, rock permeability may change due to the increase of the effective stress which could significantly affect well productivity. The main objective of this paper was to investigate stress-dependent permeability of ultra-low permeability reservoir rocks using different types of fluid media. Meanwhile, wettability and its effect on stress-sensitivity permeability were also studied in this research.

A total of twenty-seven sandstone rock samples selected from Daqing oilfield reservoir rock and Changqing outcrop rock was used to conducted permeability stress-sensitivity experiments. The gas permeability of those rock samples ranges from 0.0029mD to 7.7603mD. Experimental results indicate that gas permeability, brine permeability and oil effective permeability at irreducible water saturation all decrease with the increase of the effective stress. Most of the reduction of gas permeability and oil effective permeability takes place over the range of 2 to 16MPa effective stress. Comparative results show that reduction of brine permeability is larger than that of gas permeability over the same range of effective stress when the rock gas permeability is greater than 1mD. However, decrease of gas permeability is larger than that of brine permeability when rock gas permeability is less than 1mD. The oil effective permeability is more stress-sensitivity than gas and brine permeability. Reduction of the oil effective permeability is much greater with the increase of the effective stress when the rock samples have been aged in crude oil.

This research suggested that it may lead significantly error when gas was used as the fluid media in evaluating permeability-dependent of ultra-low permeability reservoir rock and its effect on well productivity. In addition, reservoir wettability should be considered when oil was used as the fluid media in permeability stress-sensitivity evaluation experiment.
Study on Matching Relation Between Polymer Molecular Size and Pore Size for Conglomerate Reservoir
Authors: Wenli Luo , Desheng Ma , Xiaobin Nie , Meiqin Lin , Qingxia Lin , Jian Fan , Hang Long
Published: March 2015

The matching relation between the molecular size of polymers and the pore size of Karamay conglomerate reservoir in Xinjiang oil field was studied. By employing the nuclepore film filtration method, core flooding experiments and dynamic light scattering method (DLS), the molecular size of several candidate polymers for the pilot test was examined. And several suitable polymers for different reservoirs permeability were obtained. In the microporous membrane filtration experiments, the polymer DQ3500 with the molecular weight of 3.57 × 107 matched the 0.7 mm microporous membrane well. Moreover, three polymer samples including DQ2500 (molecular weight 2.42 × 107), complex polymer BCF (molecular weight 2.42 × 107) and complex polymer ABCF (molecular weight 2.14 × 107) matched the 0.6–0.7 mm microporous membrane well. No retained aggregation was observed on the microporous membranes for all examined polymer samples. Both resistance coefficient (Fr) and residual resistance coefficient (Frr) were measured with five core polymer flooding experiments. Polymer solution including DQ3500 and DQ2500 with the concentration of 1000 mg / L were injected into the artificial cement conglomerate cores with permeability of 121 × 10-3-1000 × 10-3 µm2. The values of Fr and Frr increased with the increasing of polymer molecular weight and decreased with the increasing of core permeability. The average polymer coil hydrodynamic radius (Rh) was measured by the DLS method. The Rh ranged from 266.0 nm to 394.5 nm for the polymers with molecular weight from 2.14 × 107 to 3.57 × 107. Accordingly, the conglomerate reservoir with water permeability more than 55.4 × 10-3 µm2 could not been blocked by those polymers with molecular weight less than 3.57 × 107.
Quantitative Estimation of Gas Saturation by Frequency Dependent Avo: Numerical, Physical Modelling and Field Studies
Authors: Li Xiang-Yang , Wu Xiaoyang , Chapman Mark
Published: March 2015

It is well known that seismic amplitudes contain important information which can be related to fluid saturation. Most interpretation is based on Gassmann's theory and studies of amplitude variations with offset (AVO) with the Zoeppritz equations. However, this traditional AVO technique is often unable to make quantitative estimation of the gas saturation, hence unable to distinguish between commercial and non-commercial gas deposits. Recent attention has focussed on if the frequency response of reflections can also be used to reveal fluid information through the application of frequency-dependent AVO (FAVO), although many of these studies are based on empirical relationships and are lack of a thorough understanding of the underline mechanism and rock physics principles.

In this study, we extend the "squirt-flow" model to include the effect of gas saturation on seismic attenuation and dispersion. Combining with Wood's formula, the FAVO response can be calculated as a function of porosity and gas saturation. Therefore a model-based inversion scheme can be established by matching the calculated FAVO response to the observed ones for quantitatively estimating the gas saturation. There are three technical contributions in this approach:a theoretical frame work for modelling the FAVO response and the effects of gas saturation on seismic attenuation and dispersion;an efficient spectral decomposition algorithm for extracting the FAVO response from real data;an optimization work flow for estimating the gas saturation.

In our examples, the numerical modelling is able to predict the FAVO response to changing gas saturation which is seen in the physical modelling data, and the 3D P-wave field seismic data. Consequently we argue that with a careful model-based approach, it is possible to invert the FAVO response in terms of gas saturation. This may have important implications in the exploration of tight and unconventional gas resources.
Scale Management in Mature Gas Field: Case Study of Peciko
Authors: Bajammal F.A. , Biyanni H.M. , Riksa A.P. , Poitrenaud H.M. , Mahardhini A.
Published: March 2015

Peciko is one of the giant gas fields located in the Mahakam area, Indonesia, operated by Total E&P Indonesie. Since start up in December 1999, until May 2012, the average wellhead pressure and temperature of its wells have decreased from 150 barg to 20 barg and from 95 °C to 60 °C, respectively, while the average water/gas ratio (WGR) has increased from approximately 2.5 to 20.5 bbl/MMscf. These dramatic shifts of production parameter and borehole environment are believed to be the main factor of the increasing rate of scale deposition in significant number of its wells in the last few years. The nature of the scale encountered is mainly calcium carbonate and iron carbonate.

Reviews have been carried to better understand the phenomena of scale formation in the field and to formulate the optimum solutions in overcoming it. Guidelines have been established to facilitate early detection or prediction of scaling, which includes routine water analysis, periodic check of tubing clearance, and running multifinger caliper in the well.

Numerous attempts of removing the scale have been tried, with mechanical and/or chemical techniques, from light intervention using slick line unit, until semi-heavy intervention with coiled tubing unit (CTU). Several successful results have been observed, to some extent. Calcium carbonate scale showed to be relatively easy to remove, but the presence of iron carbonate imposes more challenge and complication. The milling operation, in particular, has been improved to minimize the negative effect of liquid circulation in sensitive wells, i.e. evolving from CTU milling using brine, to CTU milling using nitrified base oil, to electric line milling without liquid circulation.

The guidelines, lessons learned, and the foreseen solutions are considered as the key elements of scale management in the field, and will be described further in the paper.
Evaluation of Inflow Control Devices to Reduce the Water Production in Horizontal Wells of the Orinoco Heavy Oil Belt
Authors: Vasquez I.Y. , Rodriguez J.R. , Fernandez E.A.
Published: March 2015

The Orinoco Heavy Oil Belt, located in the southern part of the Eastern Basin of Venezuela, is considered the largest deposit of heavy oil in the world. It covers an area of 14 million acres and is characterized by having crude of low API gravity (from 7 to 10º), high viscosity (from 1,000 to 10,000 cp), high porosities (from 18 to 40%) and permeabilities that can reach 30 darcies. Heterogeneity is present in the Faja, there some areas with active bottom aquifers. On these particular areas an early water breakthrough has been identified in some horizontal wells.

A numerical simulation model with representative properties of an area of the Orinoco Heavy Oil Belt was defined to assess if the implementation of inflow control devices (ICDs) could reduce water production in horizontal wells. The numerical model contained a horizontal well where these completions elements were installed. The evaluation was made through a sensitivity analysis in which the configuration of the devices and some rock and fluids properties were changed. Additionally, the effect of the horizontal well length was studied as this parameter is relevant in the design and planning of horizontal wells in the Faja.

The results of this investigation indicated that the use of inflow control devices can be an effective technology to delay water breakthrough in areas where there is an active bottom aquifer with a good understanding of the geological properties and reservoir behavior. On other hand, this study showed how the differential increase in the cumulative oil of the wells decreases progressively as the horizontal well length section increases. An economic model was created to compare the different simulation scenarios.

This research serves as a basis for determining the feasibility of implementing inflow control devices as a water control technology and to obtain valuable information to designing the horizontal section of the wells.
Fault Trap Modelling and Calculation of Reserves
Authors: Zhang Xiaomin , Zhang Libin , Sun Desheng , Lin Jixiang , Kang Haixia
Published: March 2015

The evaluation of fault sealing is an important step in the calculation of fault trap reserve. When it comes to the issue of complex 3-D fault trap structures and thin reservoirs, how to appraise and calculate the reserve properly and effectively is still a subject that needs further researching. In this respect, a certain rift basin that has experienced multi-periods rift movement and evolved in a fluvial faces and braided deltaic depositional environment has been chosen as the object of our research on fault trap evaluation and calculation of reserves. The method has been preformed in the following steps. 1) The tectonic evolution and the structural characteristics of the studying area are accomplished through 3-D seismic interpretation; 2) Based on the results of the well to seismic combination, the provenance direction sedimentary system interpretation and sedimentary evolution are completed; 3) On the basis of achievements of the tectonic evolution and sedimentary evolution interpretation, the 3-D fault trap geologic model is established by spatial interpolation. A certain method invented by Li Qingzhong is employed to forecast the fault trap reserves quantitatively. Moreover, this method can be described as follows. Constrained by the seismic horizons, fault data and sedimentary isochronous interfaces, the connected sand body units in every depth slice of the 3-D fault trap geologic model can be identified automatically. Meanwhile, their sealing degree and connectivity is appraised quantitively from the top slice to the bottom slice. Finally, through quantitative calculation of reserves for fault trap, the effective forecasting of reserves has been achieved. The results of our work have testified that this appraisal method can be applied to improve the prospecting accuracy and reserve forecasting precision of fault trap reservoirs.
Successful Application of Unique Polyamine High Performance WaterBased Drilling Fluid in Bohai Bay Shale Formations
Authors: Hanyi Zhong , Zhengsong Qiu , Weian Huang , Jie Cao , Daquan Huang , Haibin Li
Published: March 2015

With the increasing demand of oil and gas resources, the drilled formations are becoming more and more complicated. Nevertheless, in the process of developing these hydrocarbon resources, wellbore instability caused by active shale hydration and dispersion is always a great challenge around the world. Therefore, it is necessary to develop a high performance water-based drilling fluid reaching into the property realm of oil-based drilling fluid but also environmentally acceptable.

This paper detailed the inhibitive properties of a novel polyamine shale hydration inhibitor SDJA-1 through bentonite inhibition test, cuttings hot-rolling dispersion test, bulk hardness test and X-ray diffraction analysis. The results show that polyamine is highly inhibitive and high temperature resistant, superior to conventional shale inhibitors.

Incorporated with shale encapsulator and lubricator, a polyamine high performance water-based drilling fluid was established based on triple inhibition. Extensive laboratory work was carried out to compare the properties of the system with other conventional inhibitive water-based drilling fluids and oil-based fluid. The results indicate that the system is highly inhibitive, rheology stable and excellently lubricant, approaching to the general oil-based drilling fluid.

Drilling in Bohai bay presents some unique challenges primarily related to wellbore instability in drilling through the highly complicated and reactive shale formations. Therefore the uniquely engineered polyamine high performance water-based drilling fluid was proposed with a special emphasis on wellbore stability. Three wells trials demonstrate that the system impart excellent performance like shale stability, trouble-free trips, and rheology stability. No bit balling is observed and ROP is improved compared to before. In conclusion, the system shows outstanding performance in all aspects and contributes to a high degree of success.
Drilling Risk Management in Offshore China: Insights and Lessons Learned from the Deepwater Horizon Incident
Authors: Cheng Rongchao , Wang Haige , Shi Li , Ge Yunhua , Sun Zhengchun , Tian Hongliang
Published: March 2015

The Deepwater Horizon disaster is undoubtedly verified as the most severe and systematic failure within the oil and gas industry to date, leaving a lasting legacy with enormous human, economic and environmental consequences. In the wake of this tragedy, CNOOC, Sinopec and CNPC are triggered with joint efforts to upgrade safety rules for shallow and deep water drilling, so as to keep up with increasingly risky operations in an increasingly tough situation in China. Especially, there is a pressing need to rebuild integrated strategy and reshape the future of offshore play in South China Sea, the major and prospective deepwater area typically featuring in HPHT and lacking of matched drilling risk control technologies.

Rigorous requirements are primarily analyzed with respect to present status of offshore drilling in China. All recorded oil spill incidents in GOM are statistically discussed to recognize controllable and uncontrollable reasons. Then, in view of the possible causes of the Deepwater Horizon accident, an integrated drilling risk management system was proposed with in-depth analysis in terms of six rules.

The primary and fundamental rule is to improve offshore drilling technology, including pressure control, wellbore profile design and adjustment, casing running, cementing, risk prediction and treatment, as well as related equipments like BOP, ROV and riser. The second is to further modify offshore drilling standards, specifications and regulations. The third is to strengthen supervision and management from both national and corporate structures. The fourth is to cultivate and intensify the safety culture within the whole drilling system. The fifth, also the most urgent, is to establish allied emergency response system for blowout, explosion and oil spill. The last is about recruiting, training and talent introduction.

The main purpose of this paper is to establish a specific drilling risk management system appropriate for offshore China to guarantee the energy security in the post-Macondo offshore play.
Seismic Data Driven Rock Physics Models and the Application to Tight Gas Saturation Estimation
Authors: Cao Hong , Yang Zhifang , Liu Jiawei , Tang Gang
Published: March 2015

Pore fluids prediction using seismic data is seldom covered in most considerable discussion in tight gas, although more interests are focused on fractures and sweet spots. Some theories based on homogeneous high porosity and permeability rocks have been widely investigated. Unfortunately, there seems to be no models published can properly describe the nonlinear relationship between saturation and P wave velocity at seismic frequency in tight reservoir, and low frequency experimental data are still scarce.

Gases always tend to gather at upper pore spaces in reservoir, resulting in saturation variation with depth due to interaction principle between buoyancy and capillary pressure. This law hence encourages us to probe into partial saturation related elastic properties through seismic data mining incorporating with experimental and logging data to indicate fluids.

Through various gas intervals oriented P wave-'saturation' data collections extracted from seismic data, new nonlinear relations are discovered, which indicate coexistence of patchy and homogeneous fluids effects, and cannot be properly explained by published models. Motivated by the complex relations of Vp-Sw at seismic frequency, a modified White's model is proposed to explain partial saturation effects in tight rocks, and updated rock physics models match the real seismic data quite well.

Case study of tight gas exploration in a Triassic basin in southwest China shows that seismic data-driven models are helpful means to reduce uncertainly in seismic interpretation and have improved the success rate of drilling by 20%.
Study on Mechanism of In-Depth Fluid Diversion by "Gel Dam" Placed with Horizontal Well Using X-ray CT
Authors: Lv Jing , Liu Yuzhang , Gao Jian , Li Yikun , Wei Falin , Li Junjian
Published: March 2015

Due to severe heterogeneity of thick positive rhythem reservoir and the gravity influence, the injected water channels and ineffectively cycles through its lower high permeability zones. For the whole reservoir, its sweep efficiency is relatively low and a huge amount of residual oil is enriched in its upper low permeable zones. The technique of in-depth fluid diversion by "gel dam" placed with horizontal well involves the injection of gel by horizontal or sidetracking wells drilled between the injection and production wells in the lower more permeable and strongly swept zones of thick positive rhythm reservoir, creating" gel dams". The injected water then will bypass the "gel dams" and be diverted into the upper low permeability zones where crude oil is relatively enriched. As a result, the sweep efficiency and oil recovery of the upper, low permeability zones can be both increased. In this paper, the EOR mechanism of the technique is studied by means of laboratory water flooding experiment combined with x-ray computer tomography(C T).

The physical model, an artificial cementing heterogeneous model casted with epoxy resin on surface, is made based on the similarity criteria for water flooding process in 2D porous media. The water flooding processes in the physical model, before and after the "gel dam' is formed, are scanned by x-ray C T at different pore volume injected, which provides a visible means for studying the EOR mechanism of the technique, through observing the distribution feature of "gel dam', tracking the oil and water distribution, water flooding streamline's change, fluid saturation distribution and its dynamic variation.

The results of water flooding experiments indicate that, with this technique, the injected water is diverted into the upper low permeability layer to displace the remaining oil therein, and the sweep efficiency and oil recovery both increase significantly. After the "gel dam" formed, the ultimate oil recovery increases by 16.7%, its water cut falls to 62.8%, and its ascending velocity slowed down.

With" gel dam" technique, gel can be placed in the deep reservoir zone to achieve in-depth fluid diversion. It will be a promising EOR method for thick positive rhythm reservoir.
Recent Advances in Oil Spill Response Technologies
Authors: Nedwed Tim
Published: March 2015

This paper discusses recent advances ExxonMobil has made in oil spill response technologies for large spills in dynamic ice conditions; however, much of the work has application in all environments.

We have developed a new dispersant that is effective at much lower dosages than currently available products. For ice conditions, we have developed a concept to utilize the propellar wash of response vessels to supply the necessary energy to more effectively disperse dispersant-treated oil.

In situ-burning has undergone extensive evaluation as an oil spill response option including a multi-year joint-industry research project evaluating a concept to enhance in situ burning in ice using chemical herders. Recent research indicates that chemical herders can also enhance in situ burning in open water. In addition, we have initiated research on a novel concept to use oleophilic skimmers in conjunction with mini floating incinerators to allow immediate in situ burning.

We are also studying tools to enhance our ability to remotely detect and track oil slicks on the water surface as well as underneath ice. For oil under ice, we have been studying the use of a helicopter-mounted nuclear magnetic resonance sensor to detect, track, and map oil location and relative density. We are also studying methods to detect and determine the thickness of oil slicks using remotely controlled helicopters.
The Controlled Freeze Zone Technology for the Development of Sour Gas Resources
Authors: Valencia J.A. , Kelman S.D.
Published: March 2015

Controlled Freeze Zone™ is an efficient single-step cryogenic distillation process for the removal of carbon dioxide, hydrogen sulfide and other impurities from natural gas. Rather than avoiding the freezing of CO2 at cryogenic temperatures, the solidification is allowed to take place, albeit in a very controlled fashion. The technology has shown the potential to more efficiently and cost-effectively separate carbon dioxide and other impurities from natural gas, and to discharge these contaminants as a high-pressure liquid stream ready for underground injection, either for enhanced oil recovery applications or for acid gas injection disposal.

Introduction

Natural gas is the cleanest burning hydrocarbon fuel available and its growing demand is only projected to rise throughout this century. ExxonMobil anticipates total global energy demand to grow 35% by 2040 relative to 20101. Greater demand for electricity accounts for more than half of this increase. The clean burning characteristics of natural gas and its increasingly competitive economics for power generation are driving its expanded use in electrical power generation. Natural gas emits up to 60 percent less CO2 than coal when generating electricity, which becomes quite significant as costs arising from greenhouse gas policies mount. ExxonMobil forecasts natural gas to emerge as the leading source of electricity generation by 2040, and to become the second largest global fuel by 2040 behind oil, displacing coal from the second spot.
Pushing the Boundary of Ultra HP/HT Completion Technology: The First 20,000-psi 470-degree F Permanent Production Packer for As-Rolled Casing
Authors: Doane James , Deng Guijun , Collins Scott , Anderson Gary , Shyu Goang-Ding
Published: March 2015

The growing global demand for hydrocarbons is the key driver for the development of high-pressure/high-temperature (HP/HT), and ultra HP/HT completion technologies. However, well completion of ultra-HPHT fields poses great technological challenges to the operator and service companies. Existing completions technology is reaching its design limits around 15,000 psi and 450°F.

As operators continue to drill in deeper and more extreme formations, the technology demand to suit these environments has steadily increased. Great efforts have been made across the industry to develop safe and reliable completion tools qualified for conditions in excess of 15,000 psi and 450°F. A new technological boundary was set recently in permanent production packer development?the first 20,000 psi, 470°F permanent production packer for as-rolled casing.

A modified ISO 14310 V3 validation test was conducted on this permanent packer in as-rolled casing ID.

The packer passed the test with no visible seal element extrusion, slip damage, or leaks detected at any of the load points in the test (including the bubble test).

This paper presents how the packer utilizes a novel seal system design that evolved from several field-proven HPHT seal systems and the ways technological challenges are addressed using state-of-the-art materials and design processes. The paper comprises conceptual design, design optimization using finite-element analysis, and material characterization for metallurgical and seal materials. The qualification testing processes for the permanent production packer are also described in detail.
Fibre Optic Sensing for Improved Wellbore Surveillance
Authors: van der Horst Juun , den Boer Hans , in 't Panhuis Peter , Kusters Roel , Roy Dayeeta , Ridge Andrew , Godfrey Alastair
Published: March 2015

Fiber Optic (FO) sensing technology is an exciting and novel technique offering many advantages over traditional wellbore surveillance methods1–3. Multiple FO cables can be installed that can be designed for sensitivity to a wide variety of signals such as temperature, pressure4–5, strain6–7, sound8, and the presence of specific chemical compounds. Permanently installed FO cables enable a cost effective surveillance policy where data acquisition surveys can be conducted without well interventions, in real-time, at any time, and continuous along the entire well bore. The avoidance of well intervention eliminates production deferment and operational risks of conventional surveys. Frequent, time-lapse FO based surveys can provide critical reservoir surveillance data for production and recovery optimization.

One instance of fiber-optic surveillance is Distributed Sensing, which uses the entire fiber as a sensing element. Recently, very good progress has been made in Distributed Acoustic Sensing (DAS) for hydraulic fracturing monitoring9, production profiling for commingled oil and gas producers, injection profiling for water injectors10, gas lift monitoring and the acquisition of wellbore seismic data such as Vertical Seismic Profile (VSP) surveys11–12. These applications are also seen to benefit from integration with other methods such as Distributed Temperature Sensing (DTS) and Distributed Pressure Sensing (DPS). In terms of wellbore surveillance, the possibility to monitor flow along the entire wellbore from FO sensing provides useful insights in the complex flow behavior in a well which can be used to optimize well performance.

There are also many improvements to be made in the enabling Distributed Sensing infrastructure such as the handling and evaluation of very large data volumes and seamless FO data transfer, the robustness & cost of the FO system installation, and the overall integration of FO surveillance into the full workflows. It will take some time before all these issues are addressed but it is clear that FO based applications will play a key role in future well and reservoir surveillance.

In this paper some examples of using DAS for Production Allocation are discussed.
Deep Water Lacustrine Architectural Elements and Subsystems Identified in the Subsurface from Borehole Images - An Example from Weizhou Field, Beibuwan Basin, South China Sea
Authors: Xuan An Xiao , Abu Bakar Mohd Nizam
Published: March 2015

Introduction

Outcrop work on deepwater deposits often shows mass-flow systems are more complicated and heterogeneous than generally accepted. However it is difficult to recognize the different architectural elements and subsystems in the subsurface at reservoir scales. At a reservoir scale, the finer details of heterogeneity are important for accurate reserves calculation, completion strategies and development well placement.

This paper describes how high-resolution resistivity borehole images are able to identify deepwater subsystems and architectural elements in the subsurface. The study sections consist of four wells located offshore Beiwuban Basin in the South China Sea (Figure 1). Borehole images were recorded in all these four wells. Detailed observations from borehole image logs reveal the occurrence of turbidites, slumps, and debrite facies in a deep-lacustrine setting. Openhole logs could not resolve the heterogeneity and different facies in the reservoir.
Integrating Digital Image Processing and Artificial Neural Network for Estimating Porosity from Thin Section
Authors: Wardaya Pongga Dikdya , Khairy Hilfan , Sum Chow Weng
Published: March 2015

Porosity estimation from thin section image using digital image processing is critical for petrography study since it gives a brief description on the 2D porosity of the sample. The standard routine uses the binarization process that converts the colour (RGB) image into a binary image using pixel value treshold. The idea is that the treshold value must accomodate all the blue regions correlate to pore and turns it into white in the resulting binary image. Errors come from mis-conversion when the matrix is converted into pores and yields larger pore spaces. This error can be larger when dealing with samples having high blue variation, for example; stained carbonate or polarized microscope captured thin section.

To address this issue, an integration of neural network and image processing is proposed to estimate accurately the porosity from a thin section. The neural network, based on color pattern difference between pores and matrix is assigned to segment them by addressing their original pixel value with a targeted code value, e.g.; 1 for pores and 0 for matrix. After the segmentation, pixel counting is then used to calculate the porosity. This method requires the training data which is the cropped region of pores and matrix. In the training process it uses the Lavenberg-Marquadt learning method.

Synthetic samples and bonafide thin sections of sandstone and stained carbonate are used for testing. For each sample the computation time is less than 10 seconds and the error, which is caused by mis-segmentation, is less than 1%. Results from standard image processing technique are also evaluated for comparison. The algorithm can also work for the grey scale image and binary image as such it is suggested that it can work for estimating microporosity in carbonates or coal from SEM image. The proposed method brings new advance in digital petrography and can be an accurate and fast tool for porosity estimation from thin sections. Furthermore, as the neural network algorithm can also segment the multi mineral matrix present in the sample (stained carbonate thin section), the fraction of each mineral constituent can also be estimated.