Verkhnechonskoye oil and gas field is characterized by complicated geological structure, which places restrictions on well profile, selection of BHA and the time required for hole conditioning prior to casing running and cementing. The objective of this paper was to run a number of experiments aimed at drilling process optimization and reduction of horizontal well construction time at Verkhnechonskoye field thanks to drilling 178-mm production casing section in one run.

The testing consisted of two phases.

In the first phase 178-mm section was drilled in two runs. At first, maximum rate of penetration was maintained before the first complicated interval – the Middle Motskaya sub-suite – was encountered. Then the assembly was pulled out of hole, and LWD tools were included in the BHA. Upon completion of drilling and during POOH standard procedures were followed, and production casing was immediately run in hole.

Then the experiment was run to drill the production casing section in one run using BHA which initially included a set of logging tools.

Both experiments were used to successfully test the downhole motor with a specially designed oil-resistant elastomer.

During the first series of experiments the time of 178-mm section drilling reduced by 12 to 30 hours, depending on the depth of production casing running.

Then, the interval was drilled in one run using LWD tools, and about two days were saved. Also, the mudstone interval remained exposed for a much shorter period (almost 2 days), which reduced the risk of caving.

Using logging tools while drilling enabled the Customer’s geology department to receive the data in real time, which gave them a better understanding TVD depth of production casing running.

The practice of drilling ahead with similar BHA including full LWD suite in other wells showed that significant depth and rigidity of the assembly made it impossible to use it, if the azimuth of the well changed by over 60°. At the casing setting depth exceeding 2700 m even without changes in azimuth, in lower intervals issues were encountered with transferring weight on bit while slide drilling, which resulted in significantly lower rate of penetration.

Another result of the experiment refers to the downhole motor with the oil-resistant elastomer. It worked throughout its warranty operating life – 147 hours of circulation – which allows recommending the motor for using with oil-based mud systems.

The experience obtained at Verkhnechonskoye field may be used at other fields with similar geology, primarily in Irkutsk region.

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