Limit analysis of extended reach drilling in South China Sea

Extended reach wells （ERWs）, especially horizontal extended reach well with a high HD （horizontal displacement） to TVD （true vertical depth） ratio, represent a frontier technology and challenge the drilling limitations. Oil and gas reservoir in beaches or lakes and offshore can be effectively exploited by using extended reach drilling （ERD） technology. This paper focuses on the difficult technological problems encountered during exploiting the Liuhua 11-1 oil field in the South China Sea, China. Emphasis is on investigating the key subjects including prediction and control of open hole limit extension in offshore ERD, prediction of casing wear and its prevention and torque reduction, φ244.5mm casing running with floating collars to control drag force, and steerable drilling modes. The basic concept of limit extension in ERD is presented and the prediction method for open hole limit extension is given in this paper. A set of advanced drilling mechanics and control technology has been established and its practical results are verified by field cases. All those efforts may be significant for further investigating and practicing ERD limit theory and control technology in the future.

A numerical method for determining the stuck point in extended reach drilling

A stuck drill string results in a major non-productive cost in extended reach drilling engineering. The first step is to determine the depth at which the sticking has occurred. Methods of measurement have been proved useful for determining the stuck points, but these operations take considerable time. As a result of the limitation with the current operational practices, calculation methods are still preferred to estimate the stuck point depth. Current analytical methods do not consider friction and are only valid for vertical rather than extended reach wells. The numerical method is established to take full account of down hole friction, tool joint, upset end of drill pipe, combination drill strings and tubular materials so that it is valid to determine the stuck point in extended reach wells. The pull test, torsion test and combined test of rotation and pulling can be used to determine the stuck point. The results show that down hole friction, tool joint, upset end of drill pipe, tubular sizes and materials have significant effects on the pull length and/or the twist angle of the stuck drill string.

EFFECT OF DRILLPIPE ROTATION ON BOREHOLE CLEANING FOR EXTENDED REACH WELL

Wellbore cleaning is a key technology for the Extended Reach Drilling （ERD）. The success of drilling extended reach wells depends directly upon the quality of wellbore cleaning. The rotation of the drillpipe, and hydraulic and rheological parameters, are the key factors for wellbore cleaning. In this study, Computational Fluid Dynamics （CFD） is applied to simulate solid-liquid two-phase flows in wellbore annulus. The annual flow field with the presence of drillpipe rotation is described through analyzing various rotation conditions. The results indicate that the quasi-spiral flow is the main flow pattern for liquid-solid transport in the horizontal annulus. The influence of rotation on the cuttings transport is also investigated, as the rotation of drillpipe increases the disturbance of liquid to solid in annulus. As a result, the solid flow becomes favorable and the solid volume is reduced. Comparisons with previously published results are also performed to prove the importance of drillpipe rotation in the wellbore clearing for the ERD.

Elaboration of a conceptual solution for the development of the Arctic shelf from seasonally flooded coastal areas

Currently,construction of facilities in the Arctic is carried out on sand islands,but there are limitations for remote coastal conditions.These restrictions are associated with the lack of quarries with construction sand in the immediate vicinity of the work site,as well as the risk of seasonal flooding of the territories.This article includes conceptual solutions for construction of modular piling in Arctic nearshore conditions,upon which drilling rigs and auxiliary equipment can be placed for the purpose of subsequent wildcatting,development and exploratory extended reach drilling wells(with measured depth about 15000 m).During the construction of the modular piling foundations,a mathematical simulation of the thermodynamic condition of the frozen ground was conducted,and the bearing capacity of the foundations was assessed.The proposed solutions will solve these problems by constructing modular pile foundations and placing the necessary infrastructure on them,taking into account the distribution of loads during operation in seasonally flooded areas.