Rheological Properties of Xanthan Gum and Polyacrylamide Mixture in Inorganic Salt Solutions

PAM is a good flocculant, and XG is a good tackifier. When the two solutions are mixed, the PAM/XG mixed solution has good viscosity and can be used as a foam stabilizer in foam drilling fluids, and it can also be used as a coupling agent for sand-fixation serous fluid. When metal cations enter the PAM/XG system, it will destroy the overall rheology and stability of the PAM/XG system. This article uses the DV3T-LV rheometer to test the rheology of different types of PAM (HPAM/CPAM/AMPAM/NPAM) and XG mixed solutions,and get the optimal test ratio. Then add various metal cations (Na+, K+, Ca2+, Mg2+) to the mixed solutions of HPAM/XG, CPAM/XG, AmPAM/XG, NPAM/XG respectively. We know divalent metal cations have greater impacts on the shear stress of the PAM/XG composite system, which is likely to cause its shear dilution. Finally, through mechanism analysis, it is concluded that it provides a good preliminary foundation for the research of foam drilling fluid and sand-fixation serous when the metal ion destroys the molecular structure of the PAM/XG composite system.

Modeling the Pressure Transverse for Foam Drilling Operation in Vertical Well

Pressure transverse in foam drilling operation is sensitive and difficult to predict particular at the start of flow that follows the unavoidable shut in due to inevitable procedure of stop and proceed arising from re-connection of additional drilling pipe to further drill depth. The practice in drilling may not enable the flow to attain steadiness flow region before running in the length of drill pipe. Most existing models in the literature for predicting pressure transverse in foam drilling operation only captured the steadiness flow region of the foam drilling operation by keeping out restriction terms induced by accumulation and kinetic for simplicity sake, hence unsteadiness flow region experienced during foam drilling operation was rarely modelled. It is highly expedient to derive a model that evident the unsteadiness region in order to accurately predict pressure transverse, hence sufficiently analyses the well stability during foam drilling operation. In this study, a model for forecasting pressure transverse in foam drilling operation was established considering restriction term caused by accumulation and kinetic that constitute for accurate formulation of hydraulic model that govern flow of foam during underbalanced drilling. By applying the proposed model to a case study reported in literature, pressure transverse at unsteadiness flow region for foam drilling operation can be quantitatively estimated and analyzed. The result obtained in a case study carried out indicates high variance in pressure as function time at the beginning of flow in foam drilling where unsteadiness is promoted before matching up closely with the results obtained from the existing Guo et al 2003 model at the steadiness flow region. The new model has a better accuracy with a percentage error of 0.74% and 6.4% as compared to previous models by Guo et al 2003. The proposed model make possible for drilling engineer to take decision with larger precision during hydraulic design of foam drilling operation and guaranteeing well stability in complex drilling system.

Effects of ROP on Selected Foam Rheological Properties in Vertical Wells

Foam drilling is one of the different techniques of underbalanced drilling which is to intentionally design the proper compressible fluid as drilling mud. The main characteristics of the foam fluids are its wide range of low densities which are generally from 1 to 5 ppg; and its high effective viscosities which are superior to those of both constituents; liquid and gas. Literature reported case stories of foam drilling in most challenging formations with excessive and complete losses due to reservoir depletion, fractured strata, unconsolidated beds etc. For good cuttings removal and desired hole cleaning, the technique of foam drilling relies upon foam high effective viscosity and annular mixture velocity. To guarantee adequate hole cleaning in foam drilling, factors affecting these two parameters must be carefully monitored and controlled during the entire hole sections. As foam rheological properties are among the most affecting parameters for hole cleaning, their detailed studies are not considered exaggerated. Carrying out foam drilling in producing formations results in annular foam rheological properties much different than those in the string due to the intrusion of formation cuttings and fluids into the annular mud stream. Therefore, detailed analysis of different parameters affecting on the annular foam rheology is crucial for optimum foam drilling. Rate of penetration (ROP) is a determinant parameter for drilling economy, but might also be one of the main causes for the changes of the annular rheology of foam. In this paper, we developed a recent program using VISUAL BASIC for a hydraulic model of foam drilling in vertical wells to investigate the influence of ROP on selected foam rheological properties. For the particular conditions in the Appendix Table of this paper, foam annular velocity, quality, density, power index, Reynolds number and cuttings concentration all increase proportionally with the increase of ROP, whereas, annular surface pressure, effective viscosity, consistency index and friction factor all decrease inversely with the ROP increase.

A Simulating Study for Back Pressure Impacts on Selected Foam Rheological Properties in Vertical Wells

In this paper, the emphasis is put on the effect of the surface back pressure on selected foam rheological properties. A hydraulic model for foam drilling in vertical well has been developed using Visual Basic program to thoroughly analyze foam hydrodynamics and to study the effect of the back pressure on these selected rheological properties such annular pressure, foam quality, density, effective viscosity, power and consistency indices and cuttings concentration along the entire annular section. The model intends to simulate and predict foam rheology and characteristic parameters for foam drilling in vertical wells. The model was evaluated and validated by running its program on two foam-drilled wells in the Middle East. The developed model was also compared with two other models: Valco-Economides’ model; and Sporker’s model. The average errors of the developed model accuracy were 2.59% and 10.85% for the first and second wells, respectively. The model accuracy was slightly better than that of Valco-Economides’ one, but less than that of the Sporker’s one.