The explosive growth of horizontal sidetrack wells drilling has led to the large-scale geosteering development to maintain such wells. It turned out to be an important issue to improve well-drilling efficiency. For effective horizontal well-drilling in the difficult geological conditions there is used logging while drilling complex, which is often more comprehensive than in the controlled directional wells. Normally there is a distance to the bit up to 20 m (non-measurement zone from the drill bit to the logging tools) for some well-logging methods resulting in a delay in decision-making and the well-drilling efficiency is less than it could be. The solution is using at-bit sensors, which allow determining the required well-logging parameter on the bit (usually it is gamma-log or electrical resistivity). A possible alternative or addition to the existing solutions might be the use of geological well testing data. However, the current level of geological well testing in Russia is in such state that it isn’t possible to rely on the received data to make decisions concerning wells geosteering. Situation is especially crucial when it comes to the geological information (sludge diagram, gas logging). Despite this, the technological parameters registered by geological well testing station are continually used for the purposes of accident-free drilling. Therefore, it was decided to come up with an algorithm by which it would be possible to predict the reservoir presence based on the drilling mechanics data (drilling technological parameters).
The article describes the algorithm that makes it possible to predict porosity and density log on a bit for Western Siberia terrigenous deposits during the rotary drilling of wells. Algorithm design is performed by adjusting the parameters of the drilling mechanics to well logging data and well log interpretation results. As a result of the adjustment a number of conceptual remarks were made concerning the different physics of analysis of rock properties for the particular point according to the drilling mechanics data and well logging data that allow to explain the processes during drilling and to predict the properties on the bit. The final algorithm requires well logging calibration during drilling the first 100-150 m of the horizontal section of the well.
References
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