Feasibility of the Bazhenov Formation Reservoir Hydrodynamic Model

Опыт изучения нефтяных месторождений, приуроченных к отложениям баженовской свиты, показывает, что продуктивность нефтенасыщенных пластов является существенно неоднородной как по площади, так и по разрезу месторождения. Выявление зон повышенной продуктивности в отложениях баженовской свиты является одной из первоочередных задач по вовлечению в разработку значительных, но трудноизвлекаемых запасов, приуроченных к отложениям баженовской свиты. С целью выявления зон повышенной продуктивности необходимо определять типы пласта-коллектора, выявлять особенности энергетического состояния залежи нефти, строить гидродинамическую модель залежи нефти в баженовской свите. The studies of the oil fields confined to the sediments of the Bazhenov formation shows that the productivity of oil-saturated formations is significantly heterogeneous both in terms of the area and thickness of the productive formations. Identification of higher productivity zones in the Bazhenov formation sediments is one of the primary problems enabling to development of the large, but hard-to-recover reserves confined to the sediments of the Bazhenov formation. To identify such zones, it is necessary to determine the type of the reservoir, identify the features of its energy state, and build a hydrodynamic model of the oil reservoir in the Bazhenov formation.

An Example of Building a Petrophysical Model of Unconsolidated Gas-Saturated Laminated Sediments Using Advanced Wireline and Logging While Drilling Services

Productive deposits of the Turonian age as part of the Kuznetsovskaya Formation are cover the eastern part of Western Siberia (Figure 1), but until recently they were not of wide industrial interest. Today, most of the gas reserves in Western Siberia are produced in the Cenomanian deposits, which are in the stage of declining production. The productivity of the deposits above Cenomanian layer has been established in many fields where the Cenomanian formations are productive. In general, in Western Siberia in the Turonian deposits, there are more than 3 trillion cubic meters of gas, which allows us to consider them as high-potential sources of gas reserves. The main difficulties in the industrial development of Turonian deposits are reduced permeability, high dissection, high content of clay fraction, high macro- and microheterogeneity of the reservoir, inconsistency of effective thicknesses in plan and section. In turn, the relatively low temperature of the reservoir predetermines the operation of the field in a mode close to hydration (Avramenko et all., 2019). Under these conditions, a good petrophysical baseline is essential to assess the exploration potential of the assets and design the development of the reservoir. Shaly gas-saturated formations are not a simple object for petrophysical modeling. Adding to this the low quality of the core material caused by the weak cementation of shallow deposits, we get a very nontrivial problem. On the other hand, modern horizontal well development scenarios dictate their requirements for petrophysical models. In other words, the petrophysical model must maintain its stability for any well logging regardless of the well trajectory (vertical or horizontal) and the logging method conveyance (wireline or while drilling). The authors of the paper carried out work on the development of a universal petrophysical model of the Turonian reservoir, for one of the fields in the region of the north of Western Siberia, based on a modern extended GIS complex.

Проблемы заколонных перетоков в скважинах с боковыми стволами и горизонтальным забоем

The article analyzes the main causes of fluid manifestations that occur in wells with side shafts and horizontal bottom at the stage of construction and operation of wells. It is established that the fluid manifestations are mainly due to the design features of such wells. The presence of overflow and interstratal overflows, in case of untimely detection and liquidation, can lead to emissions, accidents and large–scale environmental disasters. The cause of most complications at the stages of construction and operation of wells is the hydraulic connection of the drilled fluid–saturated formations with the wellbore, which accompanies all subsequent periods of well operation. To solve this problem, it is necessary to carry out repair and insulation works to eliminate overflow flows in wells with horizontal sections using blocking fluids for temporary insulation of the perforated part of the production string. Technological solutions for the elimination of intercolumn flows by pumping blocking tamponing compositions in the intervals of flow of liquids or gases, the installation of cut–off bridges to protect the productive layers from the cement material; carrying out insulation work through the upper part of the perforation zone. The authors propose the current directions of development of existing insulation technologies, taking into account the peculiarities of work in horizontal wells, in the construction of which use non–cemented shank–filters using physico–chemical and mechanical solutions. The selected technology and materials should ensure the filling of the entire porous medium and channels in the well and downhole section of rocks, as well as the optimal structure of the composition in a technologically acceptable time.

Parageneses of cryogenic formations of gas emission funnels (Part 2). Cryogenic factor in formation of gas funnels

The subject of this research is frozen rocks that compose gas emission funnels in the north of Western Siberia. The object of this research is the cryogenic factor that causes the formation of gas emission funnels. The authors substantiate the thesis that gas emission funnels are cryogenic phenomenon, and the processes preparing the explosion cannot be accurately interpreted without taking these features into account. The analysis of research materials on gas emission funnels, discovered in the north of Western Siberia, allows concluding that surface conditions may have a significant impact upon the formation of gas emission funnels. Special attention is given to consideration of the hypothesis of formation of gas emission funnels due to local heat penetration and gas supply from the depth. The necessary conditions are described. The article provides the examples of using geophysical methods for detecting of gas supply channels. It is concluded that gas emission funnels are the result of self-development of fluid-dynamic geosystems, which represent local, ice subsurface gas-saturated formations that are in a inequilibrium thermodynamic state with respect to the enclosing permafrost formations. The authors' special contribution consists in examination of the external and hidden mechanisms of the emergence of inequilibrium conditions od the mechanism that launches an explosion. The novelty of this research lies in the development of technique for determining the processes that cause the emission of underground gas, based on the analysis of cryogenic formations, which compose the walls of gas emission funnels.

Subnormality and residuals for saturated formations: A generalization of Schenkman’s theorem

Let 𝐺 be a finite group, and let 𝔉 be a hereditary saturated formation. We denote by Z F ⁢ ( G ) \mathbf{Z}_{\mathfrak{F}}(G) the product of all normal subgroups 𝑁 of 𝐺 such that every chief factor H / K H/K of 𝐺 below 𝑁 is 𝔉-central in 𝐺, that is, ( H / K ) ⋊ ( G / C G ⁢ ( H / K ) ) ∈ F (H/K)\rtimes(G/\mathbf{C}_{G}(H/K))\in\mathfrak{F} . A subgroup A ⩽ G A\leqslant G is said to be 𝔉-subnormal in the sense of Kegel, or 𝐾-𝔉-subnormal in 𝐺, if there is a subgroup chain A = A 0 ⩽ A 1 ⩽ ⋯ ⩽ A n = G A=A_{0}\leqslant A_{1}\leqslant\cdots\leqslant A_{n}=G such that either A i - 1 ⁢ ⊴ ⁢ A i A_{i-1}\trianglelefteq A_{i} or A i / ( A i - 1 ) A i ∈ F A_{i}/(A_{i-1})_{A_{i}}\in\mathfrak{F} for all i = 1 , … , n i=1,\ldots,n . In this paper, we prove the following generalization of Schenkman’s theorem on the centraliser of the nilpotent residual of a subnormal subgroup: Let 𝔉 be a hereditary saturated formation containing all nilpotent groups, and let 𝑆 be a 𝐾-𝔉-subnormal subgroup of 𝐺. If Z F ⁢ ( E ) = 1 \mathbf{Z}_{\mathfrak{F}}(E)=1 for every subgroup 𝐸 of 𝐺 such that S ⩽ E S\leqslant E , then C G ⁢ ( D ) ⩽ D \mathbf{C}_{G}(D)\leqslant D , where D = S F D=S^{\mathfrak{F}} is the 𝔉-residual of 𝑆.

3D Characterization of a Coastal Freshwater Aquifer in SE Malta (Mediterranean Sea) by Time-Domain Electromagnetics

Electromagnetic (EM) geophysical methods are well equipped to distinguish electrical resistivity contrasts between freshwater-saturated and seawater-saturated formations. Beneath the semi-arid, rapidly urbanizing island of Malta, offshore groundwater is an important potential resource but it is not known whether the regional mean sea-level aquifer (MSLA) extends offshore. To address this uncertainty, land-based alongshore and across-shore time-domain electromagnetic (TDEM) responses were acquired with the G-TEM instrument (Geonics Ltd., Mississauga, ON, Canada) and used to map the onshore structure of the aquifer. 1-D inversion results suggest that the onshore freshwater aquifer resides at 4–24 m depth, underlain by seawater-saturated formations. The freshwater aquifer thickens with distance from the coastline. We present 2D and 3D electromagnetic forward modeling based on finite-element (FE) analysis to further constrain the subsurface geometry of the onshore freshwater body. We interpret the high resistivity zones that as brackish water-saturated bodies are associated with the mean sea-level aquifer. Generally, time-domain electromagnetic (TDEM) results provide valuable onshore hydrogeological information, which can be augmented with marine and coastal transition-zone measurements to assess potential hydraulic continuity of terrestrial aquifers extending offshore.

Evaluation of NaCl and MgCl2 heat exchange fluids in a deep binary geothermal system in a sedimentary halite formation

Halite formations are attractive geothermal reservoirs due to their high heat conductivity, resulting in higher temperatures than other formations at similar depths. However, halite formations are highly reactive with undersaturated water. An understanding of the geochemical reactions that occur within a halite-saturated formations can inform decision making regarding well construction, prevention of well clogging, formation dissolution, and thermal short-circuiting. Numerical 1-D and 3-D flow and equilibrium reactive transport modeling were used to characterize the produced NaCl-brine in a well targeting a halite-saturated formation. The potential for inhibition of precipitation and dissolution using an MgCl2-brine and NaCl+MgCl2-brine were also investigated. Within the injection well, with heating from 60 to 120°C, the solubility of halite decreases resulting in the potential dissolution of 0.57 mol L-1 at the formation. Cooling from 120 to 100°C in the production well results in precipitation of 0.20 mol L-1 halite as well as anhydrite, brucite, carnallite, goergeyite, gypsum, halite, kieserite and polyhalite. Introduction of Mg2+ into the heat exchange brine resulted in a decreased potential for dissolution by 0.35 mol L-1 as the heat exchange fluid entered the formation and within the formation itself, as well as decreased precipitation within the production well, compared to the NaCl-brine. The NaCl-brine solubility was altered by changes in pressure up to 0.18 mol L-1. This indicates that designing and monitoring the composition of heat exchange fluids in highly saline environments is an important component in geothermal project design.

Reasons for low-resistant oil formations, criteria of their selection and productivity evaluation

The paper reviews the issues of low-resistivity of oil-saturated formations and analyzes the studies carried out in this direction as well. The definition of specific electric resistance plays a significant role in the selection of reservoir-beds and the evaluation of their productivity. The analysis of the complex of downhole geophysical surveys conducted in Azerbaijan territory justifies that in some cases the geological section consists of the layering of formations with anisotropic properties varying by their resistance and permeability. Neglecting such aspects in the data processing and interpretation leads to the distortions. In the definition of oil saturation of soil units consisting of sand-clay interlayers’ alternation, it is practical to consider the anisotropic nature and comparisons “resistance correlations”.