Equilibrium of an engineering string at mounting

R.I.Alimbekov

Scientific-research Institute of engineering systems "Pilot"

450000, Ufa, K.Marx st., 12, b.1

R.Kh.Rakhmatullin

Noglik drilling department, Sakhalin region, Nogliki vil.

D.M.Zaripov, A.G.Khakimov

Institute of mechanics of the Ufa Center of the Russian Academy of Sciences

450000, Ufa, K.Marx st., 12, b. 6

e-mail: hakimov@anrb.ru

 

In the north of Sakhalin the mining of oil fields of shelf of Okhotskoe sea is proceeded from a land by drilling of inclined wells with great deflections from a vertical. Three wells of oil fields Northern calotte Odoptu- sea are drilled and brought into production. A distance from a well mouth into the side of the sea should be more than 4500 m "to reach" an oil pool on the depth about 1500 m from the coast. The set of an angle was carried out from the depth 130 - 150 m, and a trajectory went to a stabilizing section at depths 1000 - 1050 m. Thus the borehole inclination was equal to 82 - 83њ. The productive oil pools were opened, as a rule, at an angle 90њ.

The balance of an engineering string in inclined well is considered. Such a problem appears at mounting with the purpose of definition of maximal length of an engineering string which can be mounted under the gravity in the drilled well; for definition of a hook load at lifting a drilling tool from inclined well.

Constructing such wells one of the most complicated and important operations is a trip of 244.5-mm engineering string.

As in the near future it is planned to drill a new well with the designed depth 6000-7000 m and with a deviation from a vertical line 5500 m, than an actual problem is the trip of 244.5-mm engineering strings in the inclined wells with large deviations from a vertical line and it requires modeling of the given technological process.

The basic equations of the element balance of the engineering string in projections on the natural axes consist of sum equations of strength and moment projects.

The deformed engineering string is settled in the drilled well which trajectory is determined by the dependence of a zenith angle and azimuth from the arc length along the borehole. The dependence of a zenith angle and azimuth from the arc length along the borehole is determined with the help of measures. The ratios for the determination of the sign angle are given.

The borehole trajectory is determined by the known dependences of a zenith angle and an azimuth from the arc length along the borehole.

The calculations conducted for the projected borehole show that the crosscutting forces in the engineering string are changed stepwise. In this case the reaction of the well walls are concentrated at the small section or have a character of a point force and it can lead to the destruction of the well walls in the indicated points. Here one can draw a conclusion: a crossover from a linear trajectory section to a well trajectory in a form of a circle should be done smoothly or a curvature of the trajectory on the crossover section should be changed according to the law of cubic polynomial.

The obtained methods and the calculation program allow to model the mounting of an engineering string and to make calculations for different values of drilling fluid densities, coefficient of sliding friction of a string on well walls, parameters of a well profile and an engineering string and efforts in a well mouth.