The development of the AV1 (1-2) reservoir of the Samotlor field is a priority because it accounts for 37% of the recoverable reserves of the deposit. Horizontal wells were proposed for this reservoir to help ensure satisfactory production figures. The primary problem associated with the drilling of horizontal wells by sidetracking is the necessity of opening the interval of unstable mudstone in the Koshayskaya suite, which is the overlapping impermeable seam AV1 (1-2). In the recent past, successful sidetracking in an extended interval of Koshayskaya clay exposed at an angle of more than 70º was considered to be a difficult task, and despite many attempts, this has not been achieved. In 2011, while drilling one of the wells using standard KCL/Polymer, an attempt was made to drill such a well. Initially, an additional inhibitor, asphalthene (a stabilizer of shales), was also added to the existing drilling mud used in sidetracking, but because of a more complex profile of traversing the Koshayskaya shale, various complications developed during drilling, precluding a trouble-free drilling process. The goal was set to solve this problem. After in-depth laboratory studies involving cuttings and cores collected during the drilling, the use of an additional reagent, a shale stabilizer, which includes a mixture of asphaltenes, gilsonite, and polyglycols with various cloud points was proposed for the existing drilling solution system. This system enabled the drilling of 32 wells with a complex profile. It also significantly reduced the construction time required for each well.
The pdf file of this paper is in Russian. To purchase the paper in English, order SPE-162082-MS.
The accidental oil spills are still one of the mostly serious problems in the Russian oil and gas complexes. But until today the approaches to the analyses of the consequences of oil spills can not be recognized as adequate, as well as the approaches to the planning and preparation to the localization and elimination of possible accidents. One of the reasons of this situation is underestimation of danger of the oil components and of the processes of their migration and transformation.
In the process of the geoecological estimation the main attention is mostly paid to the total concentrations of oil products, without considering the processes of the natural fractioning. The consequence of such approach is that the toxic properties of the oil components (incl. polycyclic aromatic hydrocarbons (PAH) and others supertoxicants) are underestimated, the environmental damages are undervaluated, the migration of hydrocarbons in the system "soil - atmosphere - grounds - plants?? is inaccurate. The oil transformation products include persistent organic compounds - the individual group of xenobiotics, which main properties are toxicity, perstistence, high migration ability and cumulativeness.
The existing equations of hydrocarbons balance suggest the vertical migration of oil products with the moisture flow in the system "soils - subsoils - capillary zone - zone of saturation??. But it doesn't taking into account that the phase transitions of substances are caused by the dominant processes: atmosphere - evaporation and chemical oxidation in soils - biooxidation and biodistruction; in grounds - sorption, diffusion; in capillary zone - formation of entrapped forms of hydrocarbons; in the zone of saturation - spreading of the lens and migration inside as a dissolved form. The age of the oil pollution, the anisotropy of the pollutants movement and their type are very important.
It is necessary to develop the system of the reliable indicators of landscapes' state, taking into account the transformation of oil products and building of the new compounds with the natural substrates, with the estimation of their toxicity and lifetime in the environment.
The multicomponent model of oil products migration with selection of the determined forms of transformation processes is proposed. The 4-zone structure of the upper part of section with oil products' forms and indicators of individual substances as well as natural fractioning processes is modeling. The geochemical markers are proposed - the final products of oxidation and biodestruction, diffusion and sorption of oil components in the environments.
The proposed solutions are necessary to use in the monitoring praxis, as well as for the selection of priority directions of remediation of the damaged landscapes. Considering the necessity of improvement of landscapes remediation efficiency, these studies are very promising.
The pdf file of this paper is in Russian.
The permeability of fissured reservoirs is characterized by a pronounced spatial anisotropy, which must be taken into account during the field exploitation [1-10]. Data on the anisotropy permeability can greatly assist in the interpretation of the results of well interference testing and hydrodynamic studies.
Earlier, we introduced a new (bloc) permeability fissured reservoirs model [11-12]. The equation for the directional permeability as a function of spherical coordinates and the two constants, determined according to the distribution of the incidence angles and trending azimuths of fissures and linear dimensions of impermeable blocks was established. The principal difference between our model and the earlier one is that, firstly, statistical distribution of orientation and the linear dimensions of the blocks were taken into account. Secondly, we examined a system of hydrodynamically interconnected fissures.
According to geophysical studies of well bores, 3D seismic measurements and core analysis, a database of spatial orientation and size of the blocks much of the productive Riphean deposit of Yurubcheno-Tokhomskoye oil field were established. This data is used to identify the directional anisotropy of permeability. In addition to the previous studies, blocks, which cross-sections at the bottom was not square, but rectangular, was examined. The ratio of the rectangle bores were determined by the number of orthogonal fissures within the reservoir studied interval.
An algorithm for the calculation of the average directional permeability, which characterizes the flow of fluid to the horizontal bore, was established. Calculations have shown that this quantity depends strongly on the azimuth of the horizontal bore. If there will be a deviation from the optimum azimuth of the bore lines, even in the (5-10)0, flow of fluid to the bore may be reduced by more then ten percent. Another practically important result that follows from the calculations, is that the optimal direction of the horizontal bore must be oriented not perpendicular to the preferred fissure (as it is currently in the engineering of horizontal well bores), but at the angle other than 900. The value of this angle depends on the anisotropy of permeability and can be calculated.
The pdf file of this paper is in Russian. To purchase the paper in English, order SPE-162053-MS.
An improved method of well-to-well connectivity evaluation is proposed. The method is based on combination of two approaches developed by now - capacitance model (CM) and Multiwell Productivity Index (MPI). Multiwell productivity index is evaluated independently of production data basing on well location geometry and average reservoir properties. Connectivity coefficients, derived from MPI are used as constrains when searching for CM solution. Following the physical meaning of the problem the capacitance model is improved by adding a constraint which was possibly overlooked by previous researches. These improves convergence of optimization problem which is inherent part of CM algorithm and enables to apply it to evaluate waterflood for real reservoir with more than 60 wells.
An injection and production rates as well as bottom-hole pressure data can yield a lot of valuable information about well interaction and therefore, reservoir characteristics, if they are analyzed properly. For example, such analysis can reveal a preferential flow direction throughout the field or quantify interaction of injector to surrounding producers that enables to reduce ineffective water circulation. Proposed method combines CM and MPI approaches which both got their own advantages and drawbacks. Capacitance Model provides quite detailed analysis and quantifies the well interaction. Thus, it allows us to learn more about the reservoir structure as well as to optimize the waterflood, but it turns out to be unstable when applied to real data. Also it misses an important constraint connected with a physical meaning of CM parameters. The stability of CM can be increased by using an MPI approach. To this effect, we use analytical MPI values in construction of a regularizing functional within the CM's algorithm.
The method was applied to one of Rosneft fields to establish well interaction pattern. Recommendations were given to improve waterflood efficiency.
This paper describes a new water shut-off approach for wells challenged by coning (changed shape of the cone of depression) by injecting the DSGA (Drilling Specialties Gelling Agent) polymer solution with an additional consolidation by cement slurry with improved properties. This approach was implemented at Samotlorskoe Field of TNK-BP Company. This project was implemented as part of pilot works on monolithic and compartmentalized terrigenous formations AV4-5 and BV8(1-3).
The technology deployment scope includes the formations with the system of induced fractures and water breakthroughs, high-permeable interlayers, bottom water, impact of displacement front of injectors. Injection of gel into formation results in a reduced volume of produced water, reduced fluid rate and increased formation drawdown in producers. Injection of gel into formation provides for an increase of pressure gradient between injection and recovery zones and change in direction of in-situ filtration flows. Oil-saturated interlayers of low permeability and watercut previously not covered by displacement are involved in the active reserve recovery process. This results in a reduced volume of produced water, reduced fluid rate and increased formation drawdown in producers.
Increase of well stream watercut is observed in mature fields. This requires deployment of technologies to limit the water inflow. At present, the sources of water inflow are controlled by various technologies — from conventional cementing to use of various mechanical packers and advanced chemicals.
Efficiency of deployed water shut-off technologies can be improved by developing and perfecting the procedures for selection of candidate wells for remedial cementing and also using the holistic execution of works.
Increased of watercut level is caused by several factors such as rise of oil-water contact, inflow of injected and edge water, casing leaks, bottom water coning and crossflows.
The watercut of well stream can be increased due to poor quality of well cementing. In this case a mud cake is formed on borehole walls interfering good adhesion of cement and rock. This mud case is washed away during the well operation that leads to fluid migration between formations.
Use of cement slurries with very low fluid loss can lead to an insufficient dehydration of slurry and consequent low quality isolation of perforations or damage of casing string. Very fast dehydration of the slurry with very high fluid loss can lead to unstable cement not able to withstand pressure drop. Poor quality of cementing results in formation of water and gas fingers during the setting time, improper adhesion of cement and casing string during the cyclic loading, uncontrolled loss of circulation. Fractures are developed in the formation during cement squeezing due to the overpressure. Lack of cement leads to fluid flow, which is aggressive to metal and becomes a reason of through corrosion holes in the casing string. Water entry causes circulation in the casing cement in the points of contact of casing joints with cement and cement with bore wall. Moreover, water ingress may occur due to lost integrity of cement caused by damaged cement plugs and casing leaks.
Typically, integrity of set cement is lost as a result of mechanical damage during tripping, expansion of casing string and compression of cement from pressure tests, expansion and compression of pipes due to cyclic changes of pressure and temperature during well operation. Moreover, integrity of set cement can be damaged by perforation that creates impact loads on casing string.
The problem of parameter assessment characterizing oil-and-gas content, and its adequacy to real data which the geologist interpreter has is considered.
The necessity to appeal to this problem is connected with the existing methods of finding such parameters don't consider:
1. the real character of geological-geophysical data and the specific errors arising at parameter assessment of oil-and-gas content and forecasting of their values;
2. the uncertainty of conclusions concerning all parameters including volumetric data of hydrocarbon reserves on the field.
One of the main tasks of oil-and-gas field geology is calculation of hydrocarbon reserves which is nowadays carried out on the basis of three-dimensional geological-geophysical models. One of the key parameters influencing accuracy of reserve calculation is an authentic definition of factors of porosity and oil content which are calculated by means of field and geophysical methods of research. The last methods don't allow establishing the size of porosity and oil content but they estimate the sizes of geophysical parameters which are connected by correlation dependences with collector properties of breeds. To find the concrete expressions of these dependences and their parameters we use statistical data processing and finally we sometimes use replacement of the real experimental material with the received laws and some integrated assessment of Correlation ratio measure, i.e. the general for all dependence as a whole. According to the accepted technology the found law in the form of the coupling equations between parameters is transferred on the studied object. This way is often the source of erroneous conclusions which can bring: from incorrectly chosen conditions of opening and modes of well operation to mistakes in drill site and the conclusions about reserves and resources of hydrocarbon raw materials in the regions.
Nowadays at constructing 3D geological- geophysical models program products IRAP RMS (ROXAR) and Petrel (Schlumberger) are widely used. They have modular systems of construction. IRAP RMS, Petrel solve practically all problems at creation geological-geophysical models. However, these tasks are solved on the already processed information which is not always objective. As a result the constructed models don't allow solving issues of certainty of reserve calculation.
The paper presents a methodology of hydrocarbon fuid composition calculation on the basis of gas and condensate profiles calculated in a black oil simulator. The methodology is based on the straight dependency of the condensate-gas factor (CGR) and the reservoir pressure (Pres). In order to determine a fluid composition a dependence function between a fraction of a hydrocarbon component and CGR is created using a PVT-simulator. Having a relationship between CGR and a hydrocarbon fraction a fluid composition can be calculated using the average CGR from black oil simulation results. This methodology gives a fraction of every individual component in comparison to composition modelling, where real components should be groupped in pseudocomponents.
Proposed methodology assumes several constraints - the methodology should be applied just for gas condensate reservoirs without oil rims and the reservoir should be developed on depletion. In the work black oil and composition simulation results were compared. The paper can be useful for reservoir engineers working with gas condensates because it allows reducing simulation time without losing information about fluid composition.
In this article, a reservoir waterflood numerical modelling problem is considered for the case when injected water salinity is different from formation water salinity, and taking into account mass transfer due to reservoir salt dilution. Based on a multiphase isothermal black oil model, a new mathematical model is proposed, taking into account the basic physical parameters of the underlying process, such as maximum salt concentration (saturated solution concentration), viscosity and water density dependence on salt concentration, porosity and permeability changes during dilution. It is assumed that dilution speed is proportional to current and saturated solution concentration difference. This model was programmed in a commercial parallel hydrodynamic reservoir simulator  and was tested on real field models, showing high numerical effectiveness.
Stenin, Vladimir (Lukoil) | Delia, Sergej (Lukoil) | Levchenko, Vladimir (Lukoil Engineering) | Vereschagin, Sergei Alexandrovich (Schlumberger) | Butula, Kreso Kurt (Schlumberger) | Enkababian, Philippe (Schlumberger)
Rakushechnoe-8 is one of the exploration wells drilled in the Northern Caspian Sea. The understanding of the geometry and performance of the propped fracture completion in the Apt formation was considered critical for the economical development
of this offshore oilfield. Because of this, and the potential risk of fracture breaking into the water zone below, no resources were spared and robust engineering methods were applied for the first time in Russian offshore operations to determine the
formation productivity without and with a hydraulic fracture completion in place. This case history will detail how a planned joint engineered approach provided critical information for the reservoir and production teams to determine the formations
potentials, ensuring at the same time reliable and safe offshore operations.
After a detailed feasibility and engineering study, a local supply vessel was converted into a stimulation vessel to meet the maritime regulation requirements and projected needs of the Russian Federation. As part of the Project Readiness Assessment,
the 4000-HHP strong frac equipment was mock-assembled on the dock, tested, and all the hazards evaluated before sailing. The joint engineering team prepared a rigorous plan for multi source data collection before, during, and after treatment
operations. The plan included running dipole cased hole acoustic measurements before and after the frac treatment, bottomhole pressure gauges, a complete mini-frac test, multiple post mini-frac temperature logging runs, production logging runs, and well testing and sampling operations before and after the frac. Finally, a novel vertical seismic profile and micro-seismic measurement was employed to further understand the hydraulic fracture behavior in the Apt formation.
The data analyzed before the main fracture treatment enabled safe placement of all 49 tons of 16/20 mesh Intermediate Strength Proppant (ISP) through the drillstem test string obtaining a Cfd = 2.7 deemed optimal for the formation.
Post frac measurements and semi numerical modeling indicated that the mechanical model created before the mini frac required some additional modifications and that the propped fracture remained within the target zone. The acoustic and
microseismic post frac measurements and well-test results correlated with the expected fracture effective half-lengths and conductivity, confirming that the preparation and execution involved with attaining accurate measurements provided significant value.
The pdf file of this paper is in Russian. To purchase the paper in English, order SPE-162032-MS.
This paper presents three innovative technologies of PGS Company for marine geophysical studies: GeoStreamerGS™ is for marine seismic operations, EM for resistivity surveys in combination with seismic survey on the same vessel, and OptoSeis™ permanent reservoir monitoring during oil or gas production.
Seismics is the major marine geophysical technique. Unfortunately, in the conventional modification its effectiveness does not exactly comply with the requirements of our time. Improvements in both the marine seismic itself, its resolution capacity and informativity, and involvement of other geophysical techniques are on the agenda today.
PGS heavily invests in development of emerging technologies. The results are not late in coming. In this paper we present three innovative technologies, which our company started to offer at the geophysical services market in the last two or three years. The direct analogues that are comparable to them in terms of effectiveness and informativity are not yet present in the market.
GeostreamerGS™ technology. The technology has become the major one in PGS in the last tree years. The main difference with the conventional marine seismics is the design and types of receivers and sources. GeoStreamer uses dual-sensor (with two types of receivers) streamers with buoyant void filler instead of traditional seismic streamers with liquid fill and piezo pressure sensors (hydrophones). Low-density solid filler of special composition ensures guaranteed environmental security in case of abnormal situation of streamer failure. Two sensors types (hydrophones and geophones or geosensors) make possible registration of two wave types, namely: pressure waves like those in the traditional marine seismic streamer (hydrophones) and particle velocity (geosensors). Due to the fact that the pressure wave reflects from the free surface with the coefficient of (-1) while the particle velocity doesn't change phase (Fig. 1), in theory, ghost waves from the water-air boundary are completely removed when these waves are summed. This leads to the reduction of signal length at source and, as consequence, to spreading the signal spectrum, which results in noticeable buildup of seismic record resolution. The technology was named Geostreamer. However, the wide range of possibilities remains for further frequency extension, because the similar effect associated with the noise events from the free surface is present at the source, too.
Suppression of this noise is performed with the use of special time and depth distribution of air-operated wave transducers. They are towed at different depths and operate with delays distributed over time, which results in the reduction of wavelet length and frequency extension. This technology was named Geosource. Combination of the two technologies has the proprietary name of GeostreamerGS. Figure 2 shows an example of comparison of two time sections and amplitude spectra records obtained with the use of traditional streamer and conventional source (a) and with the use of GeostreamerGS (b). Along with the obvious visual advantages of the record, spectrum broadening into the low-frequency region allows to improve quality of seismic inversion and, consequently build better estimates of poroperm properties using seismic data. The GeostreamerGS technology can be used both in 2D and 3D seismic surveys.
An additional advantage of technology is the ability to tow the streamer at the depths of 15 to 25 meters without compromising data quality (the usual streamer is towed at the depth of 5 to 7 m). This removes the significant part of restrictions coming from the weather conditions, as operation can proceed at the wave height up to 5-6 meters, which results in noticeable decrease in performance time and, as a consequence, work cheapening compared to the conventional seismic operations.