Microscopic properties and sealing performance of new gas drainage drilling sealing material

The geological condition of Chinese coal mines are complex and high gassy,which account for ffty percent to seventy percent.Because of the abundant pores and cracks around the drainage drilling hole,the gas concentration attenuates rapidly,and the effective gas drainage period is short.The traditional sealing materials of yellow mud and cement-sand grout will readily shrink after the drilling hole is sealed,the sealing length is short and the sealing quality is not satisfactory.Currently widely used polyurethane material will shrink when it comes into contact with water,and the price is also very high.In this study,taking cement as a base material,a novel composite sealing material mixed by expansion admixture,additive,and fbrin and coupling agent was developed and the sealing performance and expansion property of the material were also studied and analyzed.The FEI Quanta TM 250 environmental scanning electron microscope was used to investigate the microstructure of material.The results revealed that the new composite sealing material had a desirable expansion performance and a defnite fluidity convenient for grouting.The solidifed material,combining closely with the drilling wall,possessed an adequate strength and was not easy to shrink.Compared to the conventional polyurethane,the gas drainage concentration by drilling sealing exceeded 40 percent,and the sealing capacity improves5 times,the sealing effect increases signifcantly.

Multi-objective optimization of oil well drilling using elitist non-dominated sorting genetic algorithm

A multi-objective optimization of oil well drilling has been carried out using a binary coded elitist non-dominated sorting genetic algorithm.A Louisiana offshore field with abnormal formation pressure is considered for optimization.Several multi-objective optimization problems involving twoand three-objective functions were formulated and solved to fix optimal drilling variables.The important objectives are：（i） maximizing drilling depth,（ii） minimizing drilling time and （iii） minimizing drilling cost with fractional drill bit tooth wear as a constraint.Important time dependent decision variables are：（i） equivalent circulation mud density,（ii） drill bit rotation,（iii） weight on bit and （iv） Reynolds number function of circulating mud through drill bit nozzles.A set of non-dominated optimal Pareto frontier is obtained for the two-objective optimization problem whereas a non-dominated optimal Pareto surface is obtained for the three-objective optimization problem.Depending on the trade-offs involved,decision makers may select any point from the optimal Pareto frontier or optimal Pareto surface and hence corresponding values of the decision variables that may be selected for optimal drilling operation.For minimizing drilling time and drilling cost,the optimum values of the decision variables are needed to be kept at the higher values whereas the optimum values of decision variables are at the lower values for the maximization of drilling depth.

Insights into the radial water jet drilling technology-Application in a quarry

In this context, we applied the radial water jet drilling(RJD) technology to drill five horizontal holes into a quarry wall of the Gildehaus quarry close to Bad Bntheim, Germany. For testing the state-of-the-art jetting technology, a jetting experiment was performed to investigate the influence of geological heterogeneity on the jetting performance and the hole geometry, the influence of nozzle geometry and jetting pressure on the rate of penetration, and the possibility of localising the jetting nozzle utilizing acoustic activity. It is observed that the jetted holes can intersect fractures under varying angles, and the jetted holes do not follow a straight path when jetting at ambient surface condition. Cuttings from the jetting process retrieved from the holes can be used to estimate the reservoir rock permeability. Within the quarry, we did not observe a change in the rate of penetration due to jetting pressure variations.Acoustic monitoring was partially successful in estimating the nozzle location. Although the experiments were performed at ambient surface conditions, the results can give recommendations for a downhole application in deep wells.

Drilling cost optimization in a hydrocarbon field by combination of comparative and mathematical methods

In drilling operation, a large saving in time and money would be achieved by reducing the drilling time, since some of the costs are time-dependent. Drilling time could be minimized by raising the penetration rate. In the comparative optimization method, by using the records of the first drilled wells and comparing the criteria like penetration rate, cost per foot and specific energy, the drilling parameters of the next wells being drilled can be optimized in each depth interval. In the mathematical optimization technique, some numerical equations to model the penetration rate, bit wear rate and hydraulics would be used to minimize the drilling cost and time as much as possible and improve the results of the primary comparative optimization. In this research, as a case study the Iranian Khangiran gas field has been evaluated to optimize the drilling costs. A combination of the mentioned optimization techniques resulted in an optimal well which reduced the drilling time and cost considerably in comparison with the wells already drilled.

Investigation of active vibration drilling using acoustic emission and cutting size analysis

This paper describes an investigation of active bit vibration on the penetration mechanisms and bit-rock interaction for drilling with a diamond impregnated coring bit. A series of drill-off tests(DOTs) were conducted where the drilling rate-of-penetration(ROP) was measured at a series of step-wise increasing static bit thrusts or weight-on-bits(WOBs). Two active DOTs were conducted by applying 60 Hz axial vibration at the bit-rock interface using an electromagnetic vibrating table mounted underneath the drilling samples, and a passive DOT was conducted where the bit was allowed to vibrate naturally with lower amplitude due to the compliance of the drilling sample mountings. During drilling, an acoustic emission(AE) system was used to record the AE signals generated by the diamond cutter penetration and the cuttings were collected for grain size analysis. The instrumented drilling system recorded the dynamic motions of the bit-rock interface using a laser displacement sensor, a load cell, and an LVDT(linear variable differential transformer) recorded the dynamic WOB and the ROP, respectively. Calibration with the drilling system showed that rotary speed was approximately the same at any given WOB, facilitating comparison of the results at the same WOB. Analysis of the experimental results shows that the ROP of the bit at any given WOB increased with higher amplitude of axial bit-rock vibration, and the drill cuttings increased in size with a higher ROP. Spectral analysis of the AEs indicated that the higher ROP and larger cutting size were correlated with a higher AE energy and a lower AE frequency. This indicated that larger fractures were being created to generate larger cutting size. Overall, these results indicate that a greater magnitude of axial bit-rock vibration produces larger fractures and generates larger cuttings which, at the same rotary speed, results in a higher ROP.

Similarity evaluation of stratum anti-drilling ability and a new method of drill bit selection

Considering the stratum anti-drilling ability,drill bit working conditions,drill bit application effect and drill bit economic benefits,the similarity of stratum anti-drilling ability was evaluated by grey relational analysis theory to screen out candidate drill bits with reference values.A new comprehensive performance evaluation model of drill bit was established by constructing the absolute ideal solution,changing the relative distance measurement method,and introducing entropy weight to work out the closeness between the candidate drill bits and ideal drill bits and select the reasonable drill bit.Through the construction of absolute ideal solution,improvement of relative distance measurement method and introduction of entropy weight,the inherent defects of TOPSIS decision analysis method,such as non-absolute order,reverse order and unreasonable weight setting,can be overcome.Simple in calculation and easy to understand,the new bit selection method has good adaptability to drill bit selection using dynamic change drill bit database.Field application has proved that the drill bits selected by the new drill bit selection method had significant increase in average rate of penetration,low wear rate,and good compatibility with the drilled formations in actual drilling.This new method of drill bit selection can be used as a technical means to select drill bits with high efficiency,long life and good economics in oilfields.