How Can A Rotary Drilling Rig Drill Quickly?

The drilling efficiency of a rotary drilling rig refers to the ratio of the total depth of the borehole to the total time spent during normal operation. The factors that affect the drilling efficiency of a rotary drilling rig include hole depth, diameter, formation conditions, and drilling tool selection

The influence of hole depth on the drilling efficiency of rotary drilling rig

In the construction of a rotary drilling rig, each time the drill bit is filled with soil, it must be lifted and removed, and then the drilling tool lowered to the bottom of the hole. Obviously, the smaller the hole depth, the higher the efficiency. Drilling efficiency V=H, 8t,+t2+2H/V,)

From the above formula, it can be seen that when other parameters remain constant, the larger H, the smaller V. When the depth of the hole exceeds 100m, the drilling efficiency drops sharply. When the depth of the hole exceeds 120m, the drilling efficiency will be lower than other construction methods. The accident rate has sharply increased. Therefore, when carrying out ultra deep hole construction, it is recommended to use other construction methods, such as positive and negative circulation.

2. The influence of aperture on drilling efficiency of rotary drilling rig

Currently, the most commonly used rotary drilling rig is the rotary drilling rig. The bucket is hollow with two inlet doors at the bottom. When drilling, the ballast is cut into the bucket through the shovel door by cutting the drill bit. Under the thrust of the lower ballast, the upper ballast gradually rises into the barrel until it is filled. The size of the drilling diameter mainly affects drilling efficiency in two aspects. One is the speed at which the compacted soil enters the bucket, and the other is the speed at which the compacted soil rises in the bucket. Firstly, the speed at which the ballast enters the bucket door is related to the entry area of the bucket door. The larger the diameter of the borehole, the larger the entry area and speed of Doumen;

Secondly, the rising speed of the soil ballast inside the bucket is related to many factors, the most important of which is:

(1) The weight of the ballast;

(2) The adhesion between the bucket wall and the ballast soil.

Obviously, the larger the diameter of the wellbore, the heavier the weight of the ballast soil, but the adhesion between the bucket wall and the ballast soil will decrease; When the diameter of the drill bit is reduced, the weight of the ballast soil decreases, but the adhesion force between the barrel wall and the ballast soil increases.

Of course, there are other factors such as the shape of the drill pipe, the friction coefficient on the surface of the drill pipe, and the moisture content of the ballast soil, which can all affect the rate of ascent of the ballast soil. Bucket. Based on the above situation, the impact of wellbore diameter on drilling efficiency is shown in Figure 2. From the figure, it can be seen that when the wellbore diameter is less than 1m and greater than 2m, the drilling efficiency will decrease.

3. The impact of geological formations on drilling efficiency

The impact of geological formations on drilling efficiency is mainly manifested in the difficulty of the formation (drillability of the formation) and the speed of soil unloading.

3.1 Drillability of Strata

The drillability of geological formations is a complex indicator. Geological drilling experts at home and abroad classify formations based on drilling difficulty. China follows the classification method of the former Soviet Union and divides it into 12 levels. The worse the gender. Due to the lack of classification of drillability in the construction of large-diameter drilled piles, there is no unified standard and specification for drilling processes corresponding to different formations. The mechanism of gravel carrying dust during the construction of rotary drilling rig pile holes still differs from geological drilling. The rotary drilling rig mainly divides the drilled formation into large blocks of rock through cutting and excavation, and then installs them into the main body of the drill bit. It is mainly used to grind the formation into fine particles and then bring them to the surface through flushing solution. Therefore, the most important indicator of the drillability of the construction formation for a rotary drilling rig is the compressive strength of the formation. As long as the drilling pressure applied by the drilling rig is greater than the compressive strength of the formation, the drill teeth can be pressed into the formation and cut into blocks.

If the above conditions are met and other factors are optimized, the drilling efficiency can be greatly improved, such as adjusting the speed and drill tooth angle. From the above, it can be seen that the harder the formation, the lower the drilling efficiency, as the required WOB increases and the time for formation fracture increases when the pressure is constant.

3.2 Impact of Unloading Factors on Drilling Efficiency

Due to differences in the composition, structure, and moisture content of drilling layers, the viscosity of the ballast material also varies. When the ballast is filled in a bucket and unloaded from the ground, the higher the viscosity, the longer the time required to unload the soil.

4. The influence of drilling tool selection on drilling efficiency

There are many types of drill bits used in rotary drilling machines, and their structures are constantly changing. For different equipment models, construction methods, and structures, different drill bits should be selected. At present, the commonly used drill bits for rotary drilling machines are divided into the following six categories: spiral drill bits, rotary drill buckets, barrel core drill bits, expanded bottom drill bits, impact drill bits, and cone drill bits. There are many varieties in each category. The selection of drilling tools has a significant impact on the drilling efficiency of rotary drilling rigs. The most suitable drill bit should be selected based on the formation being drilled to maximize drilling efficiency.

5. The impact of drill pipe selection on drilling efficiency

The commonly used drill rods for rotary drilling rigs are divided into two types: friction type and mechanical lock type. Friction type drill rods mainly rely on the friction between the drill rod key plates to generate drilling pressure. The characteristics of this drill bit are: pressurization during drilling, no need to search for pressure points, no need to unlock when lifting the drill rod, easy operation, fast lifting and lowering speed of the drilling tool, but low pressure and high pressure. The efficiency of using this type of drill pipe in softer formations; The machine lock drill rod passes through the pressure points between the layers of the drill rod. After docking, the pressure of the power head is transmitted to the bottom of the hole to form drilling pressure. The characteristic of this type of drill rod is that the maximum weight of the drill bit can only be generated after connecting the pressure point, and the drill rod must be unlocked during lifting. The takeoff and landing speed is slow and suitable for harder formations.

The construction of rotary drilling rigs is a high-tech system engineering. Only by fully understanding equipment performance, drilling strata, site conditions, drilling tool selection, operating procedures, etc., and developing a scientific construction plan, can we prove that rotary drilling rigs have comprehensive advantages of high construction quality and efficiency.