# Prediction Technique

Drillstring drag is the cumulative force required to move the pipe up or down inside the hole. Torque is the movement required to rotate the pipe. Drag forces usually are paralleled to the string weight measured with the string rotating but not reciprocating. Measured from the rotating string weight, the pickup drag is usually vaguely greater than the slack-off drag. The magnitudes of torque and drag are related in any particular well; high drag forces and excessive torque loads usually occur together. There are various causes for excessive torque and drag, such as tight hole conditions, keyseats, differential sticking, sloughing hole, sliding wellbore friction and cuttings buildup caused by poor hole cleaning.

With the exception of sliding friction, these causes are associated with problem conditions in the wellbore. Contrarily, in wells with great hole conditions, the primary source of torque and drag is sliding friction. Torque and drag from any source tend to be more troublesome in extended-reach directional wells. In very deep, highly deviated wells, overcoming torque and drag can be vital to the successful well completion. The capability to predict frictional loads on drillpipe has two main benefits:

1. Deep, highly deviated wells can be planned to minimize torque and drag and ensure successful drilling operations to total depth.
2. A more complete knowledge of drillstring loading allows use of improved drillstring design techniques, having considered the extra forces involved.

Both torque and drag are assumed to be caused entirely by sliding friction forces that result from contact of the drillstring with the wellbore. Two factors affect sliding wellbore friction:

1. The normal contact force
2. The coefficient of friction between the contact surfaces

The product of these two factors represents the magnitude of the sliding friction force. The normal contact force between the pipe and hole wall depends on several factors such as, the effects of gravity on the pipe, the effects of tension acting through curvatures in the wellbore and even pipe bending. The sliding friction coefficient is the ratio of the friction force to the normal contact force. This factor depends on specific contacting materials and on the degree of lubrication at various places in the wellbore. However, the oil and gas industry has made many advancements technologically speaking and quite a few models have been developed for these kind of issues.

PVI’s torque and drag model, TADPRO, is designed to help remove many of the risks of a drilling program, completions design or specific tool operations. Limits in the length of a horizontal based on specific friction factors can be determined. It can evaluate the needed weight to a liner-top packer. TADPRO can analyze forces downhole and predict rig equipment specifications for torque and hookload. The model provides both versatility and accuracy in its calculations and it integrates advanced features that make it easier for our users to use.

There is a good saying in oil drilling area: “Oil’s been found where it’s been found before.” This sentence has been proven to be so true again by the recent booming of oil drilling industry around USA.

A new drilling surge is happening around USA this year. Some people called it a “miracle”. Indeed it is a miracle due to the highly developing drilling technology. Horizontal drilling and fracking are two contributors to this miracle. Now in Houston, we saw that the energy companies, oilfield contractors and even landowners are rushing again into the profitable drilling industry.

Horizontal drilling is not a new thing. This drilling technique has been a hot topic for engineers and researchers for a while, but not been widely applied until 2003. Horizontal drilling is defined in Lynn Helm’s paper as "Horizontal Drilling": "Horizontal drilling is the process of drilling a well from the surface to a subsurface location just above the target oil or gas reservoir called the “kickoff point”, then deviating the wellbore from the vertical plane around a curve to intersect the reservoir at the “entry point” with a near-horizontal inclination and remaining within the reservoir until the desired bottom hole location is reached." Horizontal drilling has been going on for years in other states besides Texas around the country, including Colorado, Wyoming, New Mexico and Alabama.

However, extended-reach directional wells are becoming more prevalent today, which means that tubulars are exposed to greater amounts of torque and drag (T&D). If this torque and drag is not evaluated properly, it’ll result in stuck pipe, pipe failures and costly fishing jobs, not even mention the effects of environment contamination.

TADPRO, a comprehensive torque and drag software developed by PVI helps remove many risks of drilling program, completion design and specific tool operation. Limits in the length of a horizontal based on specific friction factors can be determined. The ability to get needed weight to a liner-top packer can also be evaluated. With the ability to analyze forces downhole, rig equipment specifications for torque and hookload can be predicted.

With unparalleled user-friendliness and graphical outputs in the industry, TADPRO provides both versatility and accuracy in its calculations, while also integrating advanced features that make it extremely easy to use and interpret results.

Although horizontal drilling didn't draw as much attention as "fracking", it is a marvel that truly benefits the drillers, just as drilling software does.