Currently considerable part of new oil and gas fields put into production, features structurally complex low permeable reservoirs. Under complex Arctic climatic conditions, Yamal in particular, development of gas-condensate deposits seems to be especially difficult and capital intensive task. To increase projects commercial efficiency, productivity of each gas well needs to be maximized. Classic solution here is to drill vertical well (VW) with fracture. Under complicated conditions especially when developing offshore fields, where drilling unit costs are considerably higher than in already developed oil and gas bearing regions of Russia, horizontal or sub-horizontal wells (HW) with multiple fractures can be more efficient. To evaluate process efficiency under conditions of Urengoiskoe gas-condensate field, a high resolution sector reservoir model for a single well was built. The model was used to calculate production parameters for various bottomhole design variants: vertical well with fracture, horizontal well with several transverse or longitudinal fractures. In this sector model, each fracture was explicitly simulated, and in number of models minimum width of a cell containing fracture was 5 to 10 mm, which correlated with real fracture width. Analytical calculations and simulation results, considered in this paper, are indicative for a number of typical effects for gas-condensate wells, which should be given a notice: ▪Generation of condensate bank in bottomhole formation zone, leading to well productivity decline;▪Inertial effects in fracture (Forchheimer effect) caused by high gas filtration rate and also resulting in well productivity decline;▪"Straightening’ of relative permeability curves in the areas with high fluid velocity.

Most of oil and gas companies are building simulation models for its assets to planning reservoir development. However, even in those cases when the models are reliable and well calibrated to the production history, they do not always reflect the interaction between the different parts of a single system "reservoir-well-gathering system-processing facilities". In other cases when hydrodynamic models are the parts of an integrated model (IM), the models become too complex and require a long time of simulation, what mostly is not very convenient. This article provides an example of the IM building for the two formations of one of the largest oil-gas-condensate field in the world. Two large gas-condensate reservoirs are in the pilot stage. Full-field development of these reservoirs will increase hydrocarbon production by 5 times (Figure 1). To develop and optimize production plans and the development of the asset, it was decided to use the integrated model. There were considered different methodologies for constructing the unified model, which combines the reservoir models, models for wells and gathering systems and for processing facilities. Finally the best approach for this project has been selected. The initial compositional hydrodynamic models, which was matched to the production history, have been successfully converted to the Black-Oil models, while giving identical forecasts for gas and condensate and significantly reducing the simulation time. Well models were calibrated to historical data. The formation fluid in the gas gathering network was modelled using a simplified description, while in the models of processing facilities the fluid was modelling with the detailed composition. Despite of the differences in the approaches to the description of PVT properties of gas condensate in different simulators (Eclipse, Gap, Hysys), the developed Integrated Model has demonstrated consistency in the description of fluid PVT-properties. A significant reduction in time of simulation was obtained during the forecast calculations. The results of the Integrated Model were very important for the field development plan optimization, the development of which was previously limited to disparate models of reservoirs and ground infrastructure.

The Yamal region of Western Siberia holds enormous reserves of gas and condensate across many geologic layers including the Achimov deposits of the Late Jurassic and Early Cretaceous. The Achimov however, is among the most challenging layers in the Yamal area with deep bedding, very low permeability, thin laminations and abnormally high reservoir pressures that all greatly complicate the appraisal and production of hydrocarbons. In this regard, accurate formation evaluation is essential to ensure efficient and economically reasonable methods of production. Modern methods of openhole logging, including NMR, acoustic and wireline formation testers (WFT) provide advanced information about the formation and can aid in the most efficient development. In this article we present the results of advanced methods of openhole logging that provides greater understanding of the characteristics of the Achimov reservoir. Special NMR measurements were used to estimate the residual fluid saturation which was confirmed with WFT tools designed for downhole fluid analysis and sampling. We also show how to overcome the negative impact of supercharging on measurements of formation pressure in the Achimov formations and the necessity of carrying out such measurements to validate the hydrodynamic reservoir model. To understand the validity of the samples acquired downhole a simulation was carried out further showing the range of possible variations of the basic PVT properties of hydrocarbons during the sampling. The results of advanced acoustic logging allows to estimate the anisotropy of the mechanical properties of the Achimov layers. The use of the data allowed us to model the fractures resulting from hydraulic stimulation and showed significant differences in the geometric characteristics of the fracture between wells and explains why the lower section of the Achimov are often depleted with respect to the upper sections.

No abstract

The key economic drivers for the development of several oil fields in the North Yamal-Nenets region were the commissioning of the main oil pipeline "Zapolyarye-Purpe-Samotlor", as well as a regional tax exemption regulation applicable to the mineral extraction tax, valid until the end of 2021. At the same time, the economic decline in 2008 and 2014 forced many oil companies to reconsider their production programs in the region. As a result, geological assessments and operational drilling programs in many fields were postponed, especially studies on complex development sites such as oil rims. As economic conditions for the oil and gas industry improved, the production activity began to increase. However, a continuation of proven work processes revealed disadvantages to meet short term economic targets. A quick assessment showed that a traditional approach to studying geological structures and assessing the current state of oil fringes would be too time consuming. Long study periods will lead to the fact that the main volume of oil will be extracted beyond the horizon of the tax exemptions, which would make projects uneconomical and jeopardizes the implementation plans for filling the new main oil pipeline.