Geological Stratification Method when Drilling with PDC Rock Bit

Ⅰ. Logging work when the PDC rock bit is used

Retrieving cuttings is one of the important links in the field logging work, and it also provides basic conditions for the application of other logging methods. The application of PDC rock bits will make the particle size of the cuttings too small, and the cuttings samples will be powdery.

According to the change of the sand returning of the vibrating screen, the docking sample position should be flexibly adjusted. If the amount of sand returning is too small, the gauze of the vibrating screen should be adjusted and used to reduce the loss of fine real cuttings.

When cleaning the cuttings samples, the cleaning water flow should be as small as possible, stirring gently, and after sedimentation, the muddy water should be poured out and then washed, so as to avoid the real cuttings being too fine and in the sample cleaning process. lost in.

The use of PDC rock bits in drilling work brings great trouble to the detection of oil and gas in logging work, because when the PDC rock bits are drilling the formation, the degree of smashing of cuttings is relatively large.

The crushing of the cuttings will make the oil and gas dispersed in the drilling fluid, and the dispersion speed is extremely fast, so that it is extremely difficult to find oil and gas in the cuttings particles.

Even using fluoroscopy is difficult and the findings are small, which makes the test results very different from the actual situation.

Therefore, using a PDC rock bit in the process of rapid drilling and applying traditional fluorescence inspection results cannot truly reflect the actual oil and gas conditions.

When encountering sandstone with no display, the hydrocarbon concentration content of mixed sample analysis is often higher than that of picking sample detection, and its hydrocarbon concentration value is often higher than that of oil-bearing formations.

At this time, the effect of using the mixed sample detection method is better than that of the selected sample detection method. A high-quality mixed sample of the display layer can clearly reflect the actual state of the formation. By combining other logging methods to interpret the formation, a good display layer analysis effect can be obtained.

Ⅱ. Lithology description homing in the drilling process of PDC rock bit

1. In the description of cuttings, we found that the WOB is sometimes a drilling parameter that cannot be ignored, and sometimes due to human factors or engineering deflection requirements, the WOB is artificially increased or decreased, resulting in abnormal drilling relative to the formation, displacement occurs due to the homing of traditional strata when drilling.

Sometimes there is no big change during drilling, but the bit WOB has a big change, and when new cuttings appear, the WOB parameters can be referred to, and sometimes the WOB size and lithology can also form a good corresponding relationship.

2. The role of torque

It has been found in practice that when using PDC rock bits, the shape of the torque curve is closely related to the lithology. The torque curve of the roller cone bit is relatively straight, generally the torque value of limestone is low, and the torque value of dolomite is high, but the high frequency and high amplitude oscillation curve appears in the later period of the bit.

On the other hand, the PDC rock bit is different. When it first encounters dolomite, a high-frequency and high-amplitude oscillation curve appears, and the oscillation frequency and amplitude of the curve are closely related to the lithology.

Limestone shows a flat curve or a small amplitude; low frequency oscillation, dolomite shows a high amplitude oscillation curve, and as the lithology changes from fine to coarse, the oscillation frequency and amplitude of the torque curve also tend to increase.

In addition, in the later period of use of the PDC rock bit, the general torque value increases, but the frequency and amplitude of the curve oscillation decrease.

3. Application of speed

Although the driller gives the rated speed, the instantaneous speed displayed on the speed sensor is ever-changing. The amplitude frequency of the rotational speed curve has a certain consistency with the change of the amplitude frequency of the torque curve, so the rotational speed change reflects the lithology change like the torque.

Different from the torque curve, the rotational speed curve oscillates symmetrically around a relatively fixed value. The oscillation amplitude becomes larger when drilling into dolomite, and becomes smaller when it encounters limestone.

The oscillation axis of the torque curve is curved, and its axis value changes with the change of lithology, and the rotational speed oscillation axis is a vertical line.

Strengthening the research on the geological stratification of PDC rock bit drilling can make the drilling work more perfect, which is a very practical research.