A Real Mathematical Model to Compute the PDC Cutter Wear Value to Terminate PDC Bit Run

Abstract

Drilling operations became more expensive and complicated day by day due to many reasons affecting directly the daily drilling cost. One of the most effective cost reductions was the fixed cutter bit solution which effectively achieved higher drilling progress and reduces overall well cost. Also, in some cases PDC bit may raise the well cost due to slow down in the penetration rate or stopped drilling to retrieve mechanical parts from the hole due to bit fatigue and followed by extra trips for junking or fishing operations. The present study focuses on most of the factors affecting fixed cutter bit design, drilling parameters that influence the bit cutting structure wear and led to the bit poor progress. All previous PDC bit mathematical models used before for determining the cutters wear value not considered real methodology on rig site to assure cutters wear and gives a proper decision to terminate the PDC bit run. Study investigated four mathematical models had calculated the PDC cutters wear using the influences of the rock strength, rock temperature and mechanical drilling parameters. These models are theoretical and applied within the lab test devices, most of models not achieved significant benefit to use in rig site applications. New model had developed to compute PDC wear value as function of surface torque arises from the friction between the drill string, bit interaction with well bore and rock on bottom. Both resistance created by the string and bit are converted to output data realized by the gauge in front the driller in rig floor and mud logging unit. Analog or digital data reflects the torque obtained from rotating the bottom hole assembly (Drill pipe, string stabilizer and bit) against the wall of hole and formation strength. Mathematical model calculates the theoretical torque for string tool joint, stabilizer and PDC bit cutters allocated in nose up to gauge area. In reality, when BHA rotates off bottom torque created is representing the summation of string tool joint and stabilizer. An additional torque realizes on surface when BHA on bottom and WOB applied then this bit torque value will be compared by model bit torque. This later obtained bit torque percentage that represents the cutters wear value preoperational to cutter height. New mathematical model had created visual analog graphs will help to take decision when stop drilling and terminate the PDC bit run. Field validation test had run in two main concessions in Egypt Western desert and Gulf of Suez with total 6 PDC bit runs using different bit size, type, cutter sizes and different bottom hole assembly (Rotary-steerable). The filed results showed significant correction in cutter wear magnitude between the model calculation and field runs, this error factor less than 10% in hard formation and less than 20% in medium to soft formations. Author set the correction in model and treated in easy way to be used on field by driller and drilling engineers to help them how to determine the PDC bit cutting structure wear value.

Mathematical modelling of performance and wear prediction of PDC drill bits: Impact of bit profile, bit hydraulic, and rock strength

“…The previous studies (Gouda et al, 2011, Pryhorovska, 2017, Wojtanowicz and Kuru, 1993 carried out on the analysis of rock-bit interaction suggested good hole cleaning. Besides, Kuru (1990) confirmed that the diamond compact material loses strength at a temperature above 350ºC resulting from high friction generated at the interface.…”

“…The objective of their work was to analyse the vertical and horizontal forces based on the cutting depth, however, they ignored the effect of mud hydraulic. Gouda et al (2011) developed a mathematical model to estimate the PDC cutters wear by including the torque obtained from drill pipe, string stabilizer, and the bit. The model was valid for certain back and side rack angles.…”

Failure analysis and optimum structure design of PDC cutter

“…2. Poor thermal stability of PCD, namely the stability of polycrystalline will be fully destroyed when the temperature of the PDC cutters exceeds 1200°C during cutting [17], to cause changes to the texture and impairment to performance [18]. 3.…”

“…The cutter suffered by the load can be decomposed into three space vectors: the vertical loads opposites WOB direction is Pa, the tangential load that opposite to the cutter movement direction of the cutter is Pt, and the lateral load is Ph. The sum of all the load projection is balanced with WOB [18].…”

An Analytical Model Coupled With Data Analytics to Estimate PDC Bit Wear

“…Usually, either an analytical model (Gouda et al, 2011) or real-time data analytics (Rashidi et al 2010) are used separately to estimate and predict bit wear. Combining both methods and using them simultaneously is thought to be an efficient approach.…”