DRILLING DELAYS

Poverty Bay Herald, Volume LXV, Issue 19820, 23 December 1938, Page 4

DRILLING DELAYS

TOTANGI OIL BORE LOSS OP VERTICALITY RECEMENTING COMPLETED HOLIDAY CLOSE-DOWN Officials of the New Zealand Petroleum Company, Limited, in charge of t'he oil exploration scheme at the Totangi iDome, Ngatapa, have not had their early hopes realised in Connection with the effort to restore the lost verticality of the hole. Fbr a time, after the Christmas close-down, drilling will proceed slowly and cautiously, in a renewed effort to straighten the well, which is reported to have taken a deviation of between four and five degrees from the vertical.

The deviation is not a matter of great significance in itself, but the company ils anxious to overcome the early deflection, in order to ensure that the test of the Totangi Dome is complete. If. the deflection should continue, and become aggravated, the value of fhc exploratory work undertaken will suffer. There are several technical reasons for endeavouring, at this stage, to correct the deflection. At the same time it is emphasised that the difficulty now encountered is of a routine character, familiar to all drilling experts, and frequently encountered and overcome in all drilling fields. It is especially likely to occur in “deep-dip” geological structures, (where the strata take steep angles, as in the case of the Totangi Dome. Hard Sandstone Strata The strata through which (tire drill is working are mainly of hard sandstone, with occasional alternations of lighter rock, and the angle at which they lie is acutely opposed to the direction of the drill. The tendency of the drill to move off the vertical line had been noted early in the process of sinking the well, but only recently did it assume proportions calling for special attention. The customary first remedy for this difficulty is to fill the hole with cement to the point where the deflection becomes noticeable, and after an interval to allow the cement to harden, to re-drill that portion of the hole.

If the cementing process is successful, the drill will usually correct its own line on meeting the opposition of the cement.

In the first effort at cementing, success was not achieved, however, and after the first few feet had been gained, the drill slipped into its old Channel and began to take out the cement, which had not fully set. The officials found that cementing at a depth of 2000 ft. to 2400 ft. has its own particular difficulties in this country, the chief of which is to secure a setting harder than the rock strata. Second Endeavour Launched

A second endeavour to overcome the deflection is now proceeding, the bottom of the hole having been refilled with cement to about 2300 ft., and this filling will be left until Wednesday next, when drilling will be resumed with a small pilot bit. The enlargement of the hole to the maximum diameter will be undertaken later, when the success or non-suecess of this system is known. There is no occasion, however, to expect a prolonged cessation of drilling operations, even should it be impossible at this stage to correct the deflection. If necessary, the hole will be deepened further, and when a softer series of strata are encountered, corrective m 'Xipures will be applied, with a fair prospect of success.

Such operations are in the normal experience of oil-well operations, and the officials are confident that they can take the well down to the desired geological horizons with a minimum of deviation from verticality. There are on record many instances in which holes have been drilled at an angle deliberately, and in country where the geological formation is suitable, the degree of deviation can be controlled within close margins. The hard sandstone strata encountered at Totangi present a problem not by any means novel, but calling for the utmost care in its handling. The, worst development that cotild happen would be an aggravation of the deflection to a degree which would prevent penetration of the structure known as the Totangi Dome. If the drill were allowed to slip down the flanks of this structure, it would finish up outside the area wherein lie the best prospects of oil production.