Multilateral Well Placement in Carbonates of Volga-Ural Region in Russia
Authors: Sayfitdinova Valentina Aleksandrovna , Dudareva Inessa Konstantinovna , Skorikova Evgenia Olegovna , Bariakh Vadim Aleksandrovich , Permyakov Vladimir Georgievich 
Published: September 2020

A substantial part of the residual reserves of theVolga-Ural region oil and gas fields (Russia) is associated with objects with a complex geological structure and reduced productivity. Cost-effective development of such objects became possible with the introduction of modern oil production technologies. One of them is the drilling of wells with complex completion, primarily horizontal and multilateral. The article describes the experience of horizontal multilateral drilling in carbonate deposits using the technology of laterolog resistivity borehole imaging. The effectiveness of multilateral wells regarding reducing geological uncertainties and the success of commissioning is analyzed.

The main part of the multilateral wells under consideration was drilled within the Upper Visean-Bashkir carbonate oil and gas complex, where reservoir properties are characterized by significant variability both in area and in section. The structural plan, despite the presence of some general regional patterns, is subject to significant changes within local uplifts. For geological support, we used the methodology for updating structural surfaces and the geosteering model during the sequential drilling of each of the borehole of multilateral well. The update was made before drilling each subsequent wellbore according to the results of the previous one. The input information for the refinement of the section was the structural dips allocated in real time according to the resistivity image of the borehole wall. This made it possible to reduce geological uncertainties and position the all boreholes in the target zone.

As an illustration of the experience of the described methodology, the article considers three multilateral wells drilled in carbonate deposits of the Bashkir and Serpukhov stages. An analysis of the drilled wells confirms the effectiveness of the multilateral drilling in reducing the risks of drilling a well outside of productive intervals due to the consistent refinement of the geosteering model based on the results of the construction of each of the wellbore.

In certain cases, it is also advisable to use the multilateral geosteering strategy, in which the first well penetrates the formation at maximum vertical depth to localize the most productive intervals, and subsequent horizontal sections are located within the intervals of the best reservoir properties encountered during drilling of the first section. In this regard, the application of the technology of the wellbore laterolog resistivity images can also be used to solve the problem of drilling the maximum thickness of the reservoir. The second and subsequent boreholes alternatively couldbe placed with penetration to the maximum vertical depth as well, to engage in the productionas many oil-saturated interlayers as it possible.

The optimal trajectory profiles, advanced logging methods during drilling and suit for purpose well placement strategyall together can ensured an increase of reservoir exposure despite the deterioration of geological conditions. The use of an integrated approach to the design and construction of multilateral wells makes their drilling useful not only to clarify the geological features of the target zone, but also to solve a number of technological issues. Thus, a successful multilateral well can serve as an alternative to multi-stage hydraulic fracturing and contribute to more uniform production compared to single horizontal wells.