Well drilling in permafrost regions: dynamics of the thawed zone

Abstract

In the cold regions, warm mud is usually used to drill deep wells. This mud causes formation thawing around wells, and as a rule is an uncertain parameter. For frozen soils, ice serves as a cementing material, so the strength of frozen soils is significantly reduced at the ice–water transition. If the thawing soil cannot withstand the load of overlying layers, consolidation will take place, and the corresponding settlement can cause significant surface shifts. Therefore, for long-term drilling or oil/gas production, the radius of thawing should be estimated to predict platform stability and the integrity of the well. It is known that physical properties of formations are drastically changed at the thawing–freezing transition. When interpreting geophysical logs, it is therefore important to know the radius of thawing and its dynamics during drilling and shut-in periods. We have shown earlier that for a cylindrical system the position of the phase interface in the Stefan problem can be approximated through two functions: one function determines the position of the melting-temperature isotherm in the problem without phase transitions, and the second function does not depend on time. For the drilling period, we will use this approach to estimate the radius of thawing. For the shut-in period, we will utilize an empirical equation based on the results of numerical modelling.

The Possibility of Estimating the Permafrost’s Porosity In Situ in the Hydrocarbon Industry and Environment

“…Thawing permafrost because of global warming creates severe problems in the cold regions of industrial development [1], including areas of hydrocarbon searching and exploration [2]. For successive hydrocarbon exploration in cold regions and prospecting for new deposits, it is helpful to know some permafrost parameters (firstly, porosity) [3]. Thawing permafrost also creates specific difficulties for industrial and residential areas e.g., Refs.…”

“…Only three temperature logs taken after the freeze-back were completed and are needed to apply this method. The conducted numerical modeling indicates that the dimensionless time of refreezing can be expressed as a function of two dimensionless parameters: radius of thawing and latent heat density [3,19]. From the last parameter, the porosity of formations can be estimated.…”

Calculation of thermal conductivity coefficient of a binary mixture

“…The impact of thermal conditions on reliability and safety of exploitation of civil engineering structures has been widely researched [1][2][3] and is in the focus of attention [4][5][6]. It was noted that to increase the reliability and safety of linear structures, such as roads, in the permafrost area, it is necessary to consider the influence of the thermal factor on the exploitation characteristics of the road surfaces and foundations during the design and construction stages [7][8][9].…”