Successful Use of a Synthetic Drilling Fluid in Eastern Venezuela

Abstract

Increased drilling performance and low mud consumption rates have made it economical to drill with an environmentally responsible, synthetic drilling fluid in the Orinoco River Delta, Eastern Venezuela. Initially, water based muds were used. Troublesome shales and claystones, coupled with complex tectonic stresses, were cause for numerous hole cleaning and wellbore instability incidents. It was decided to utilize an invert mud with the knowledge that this would inhibit the swelling mechanism of shales and reduce the hydraulic invasion of filtrate into the shale. A synthetic system was chosen for environmental impact concerns, even though the rigs were operating at zero discharge of drilling wastes. This paper details the reasons for the use of a synthetic based drilling fluid and discusses the planning and implementation of the enhanced drilling fluid programme which ultimately led to a step change in drilling performance. The paper also discusses the utilisation of an Alliance Team and the various Alliance networks to deliver solutions to the challenges faced. The results have been excellent: zero spills, improved drilling performance and world class consumption rates. Hole stability has greatly improved with mud densities identical to those previously used for near vertical wells. Since introduction of synthetic fluids, mud density profiles are designed relative to balancing pore pressures, as the rock/water base drilling fluid chemical interaction factor has been reduced.

Prediction of Mud Pressures for the Stability of Wellbores Drilled in Transversely Isotropic Rocks

“…For our purposes, we selected the weakness plane model which is linear and characterized by two constant strength parameters: the cohesion and the friction angle of the weakness planes. To date, the weakness plane model seems to be the most widely used for predicting mud pressures in wellbores drilled in anisotropic rocks ( [4][5][6][7][8][9][11][12][13][14][15][16][17][18][19][20]). This is probably because the cohesion and the friction angle of the discontinuities can be directly determined by direct shear tests.…”

“…Table 3 reports the types of analyses that we performed. 3 Hoek and Brown criterion; 4 Nova and Zaninetti criterion.…”

“…Twynam et al [4] reviewed drilling problems in the South-West area of the Pedernales Field, and observed that fewer or no drilling problems were experienced in wells where deviations were modest and the presence of the intra-reservoir shales was not relevant, while serious instability was encountered at higher deviations with significant presence of intra-reservoir shales. Furthermore, drilling mud weight data showed a relevant dependence on well deviation and a minor correlation with wellbore azimuth [4,5]. Based on drilling data, an empirical relationship between the minimum mud pressures Pe required for the stability and well deviation i, was proposed: Table 4 reports the data of the Pedernales Field.…”

“…Last and Mc Lean [3], Twynam et al [4], and Willson et al [5] analyzed wellbore failure in the Cusiana Field (Colombia) and the Pedernales Field (Venezuela). Instability occurred when drilling in the intra-reservoir shales, which are characterized by fissility and natural fractures.…”

Usage of Nano Silica in Synthetic Based Mud: A Comparison Study for High Temperature High Pressure Well

“…SBM is another type of OBM but it uses a better base fluid which results in lesser environmental issue. It various advantages, such that, higher rate of penetration (ROP), good wellbore stability particularly in shale formation, and lower torque/drag for drill string rotation, has made this mud is preferable [10][11][12].…”