The relationship between drilling quality,speed and influencing factors

The factors affecting the drilling speed are mainly geological and engineering factors. Along with China’s oil and gas industry has entered the late stage of development, how to improve the drilling efficiency has become an important weight in oil and gas fields. In oil and gas exploration, drilling is a huge and important process, so the speed of drilling directly affects the development process of the oil and gas industry. However, due to many factors, the drilling speed is not satisfactory.

Impact of drilling tools on drilling quality and speed

    However, the drilling speed of this traditional drilling method is very low, which is not suitable for today’s rapidly developing oil and gas industry. In order to improve the drilling speed, a composite drilling method of “PDC bit + downhole power drilling tool + rotary drilling” is available, which has the following advantages:　　

1. Since the drilling speed of the composite drilling bit is twice as fast as the drilling rig’s Ⅱ speed and nearly 4 times as fast as the Ⅰ speed, it is easy to increase the mechanical drilling speed significantly.
2. The high speed of composite drilling is suitable for the cutting characteristics of the PDC bit to shear the formation.
3. Smooth borehole trajectory. The combination of guided drilling and sliding drilling with interval change is easy to control the dogleg degree and ensure downhole safety.
4. The drilling tool structure is effectively simplified. The drilling pressure is generally less than 100-120kN during composite drilling, so the drilling requirements can be completing with less or no drill collar, and the chance of sticky jam is greatly reducing.
5. High-efficiency PDC bit with power drilling tools can avoid the failure of tooth wheel bearing at high speed, and the accident of dropping tooth wheel will not happen.
6. Guided drilling tool structure can be more advantageous if MWD is used to monitor the borehole trajectory. It will be more obvious to improve the drilling speed by using downhole power drilling tool compound drilling technology in deep and medium-deep formations.

Influence of drilling parameters on drilling quality speed

     In the drilling process, the influence of drilling parameters among controllable factors on drilling speed cannot be ignored, such as: drill bit type, drill nozzle diameter, drill water power, drilling pressure, rotational speed, pump pressure and discharge volume. Under certain objective conditions, the mechanical drilling speed is usually increased by controlling the drilling pressure, rotational speed, pump pressure and displacement. Generally speaking, the higher the drilling pressure and the higher the rotating speed, the higher the mechanical drilling speed will be. And the general rule is that the upper strata are more sensitive to the rotational speed and the lower strata are more sensitive to the drilling pressure. Therefore, when drilling into the soft strata in the upper part, low drilling pressure and high rotational speed are used; when drilling into the hard strata in the lower part, high drilling pressure and low rotational speed are used.

If the drilling pressure or speed is not controlling properly, it will affect the mechanical drilling speed on the one hand, and increase the wear of the drill bit on the other hand.

Which will affect the service life of the drill bit. While considering the drilling pressure and rotational speing, the pump pressure should also be adjusting, which should not be too big or too small, but the proper pump pressure is the best. If the pump pressure is too small, the rock chips broken at the bottom of the well cannot be returning in time, resulting in the secondary crushing of the rock chips;

If the pump pressure is too large, the differential pressure at the bottom of the well is generating, and the differential pressure at the bottom of the well has a pressure-holding effect on the rock chips just broken, which hinders the timely removal of the rock chips at the bottom of the well and affects the rock-breaking efficiency of the drill bit. In short, the drilling parameters should be adjusting according to the actual situation in the drilling process, and only in this way can the drilling be carring out at high speing and effectively.

The impact of drilling fluids on drilling quality and speed

Drilling fluid is the blood of drilling, so the performance of drilling fluid is crucial to drilling. The main factors affecting the mechanical drilling speed are the viscosity of the drilling fluid, the density of the drilling fluid and the solid phase content of the drilling fluid. In view of the fact that the existing deep well fluid system uses treatment agents rich in chromium ions and other heavy metal ions that have great impact on the environment, it is recommending to study and apply environmentally friendly deep well drilling fluid systems, improve the silicate drilling fluid systems and synthetic-based drilling systems that are currently using in a small scale in China, and form a series of deep well environmentally friendly drilling fluids that can adapt to the geological and engineering conditions of each drilling region.

The current deep well drilling fluid testing means.

Testing equipment is far from meeting the requirements of deep wells, it is recommending to improve the supporting series of deep well drilling fluid testing instruments capable of detecting clay capacity limit, shale stability, etc., so that the site of deep well testing to a new level.　

1. Drilling fluid viscosity If the drilling fluid viscosity increases, it will increase the pressure drop in the annulus, so that the differential pressure at the bottom of the well increases and the drilling speed decreases; the drilling fluid viscosity increases, the pressure consumption in the drilling column increases, the pressure drop of the drill bit decreases when the pump pressure is certain, the power of the drill bit decreases, the ability to clear and break the rock decreases, and the drilling speed decreases. If the drilling fluid viscosity is too small, it will reduce the sand carrying capacity of the drilling fluid, so that the rock chips cannot return to the wellhead in time, which will affect the drilling speed.
2. Drilling fluid density The higher the drilling fluid density, the higher the fluid column pressure in the well. If the fluid column pressure in the well is greater than the formation void pressure, a positive pressure difference is generating. Under the effect of the positive pressure difference, it is difficult for the rock chips to leave the bottom of the well, resulting in repeated crushing and lower drilling speed. If the density is too small to hold down the downhole fluid, it may lead to the risk of well blowout.
3. Solid phase content in drilling fluid Solid phase content has a serious impact on drilling speed and bit consumption. Half of them should try to use low solid phase drilling fluid with solid phase content less than 4%.

Impact of Drilling Equipment on Drilling Quality and Speed

The impact of drilling equipment on drilling speed should not be overlooking. In the drilling cycle of a well, the majority of the drilling cycle is extending due to equipment problems. The impact of equipment is broadly dividing into the following cases:

1. The rig configuration does not meet the drilling needs, such as insufficient rig power and insufficient hardness of the drill bit.　　
2. The equipment is not regularly maintaining and overhauling, and often breaks down and delays the schedule, such as repeating breakdowns of diesel engines, mud pumps, air pumps and other large equipment at individual well locations.
3. The drilling tools are old and the performance is declining, which increases the frequency of downhole accidents, such as the occurrence of 1 drill collar disengagement, 1 drill pipe disengagement and 2 drill pipe breakage.
4. The well site is not fully equipping with common tools and delays, such as individual well sites repeatedly broken drilling tools without salvage tools male and female cone; no spare drill bits. The existing drilling fluid system in deep wells and ultra-deep wells generally has an encapsulant whose temperature resistance does not meet the design requirements.

Other influencing factors

Since the drilling blocks are basically located in special geographic locations such as hills and deserts where transportation is difficult, it is difficult to deliver the necessary materials to the well site during rainy and snowy weather, which in turn delays the construction schedule. When it rains, water and diesel fuel cannot be suppliing in time, which also seriously affects the construction schedule. In response to this situation, we stockpiled enough water and diesel fuel in advance to avoid delays due to lack of water and diesel fuel in rainy and snowy weather.

Prevention and treatment of deep well complications, deep wells may encounter more complications than shallow wells, in the prevention of common complications and accidents such as well surge, well leakage, well collapse, shrinkage, broken drilling tools, etc., as long as the existing technology is using well and the work is done in detail, it is fully capable of achieving safe production.

Prevention of complex technology downhole, chemical collapse prevention as the main, physical collapse prevention as a supplement. That is, inhibit clay dispersion, control water loss, improve the performance of drilling fluids; adhere to the use of solid control equipment to remove sand and replenish soil, weight, while drilling and scratch, end up long up combined with refurbishment of the well wall, starting drilling before playing heavy mud plug to maintain the equivalent density of the wellbore. However, when dealing with these accidents and complications, the difficulty and danger are much greater than in shallow wells, and different measures need to be taken for different areas and downhole conditions, and the work experience of other wells should never be rigidly appliing.