Effect of reservoir characteristics and chemicals on filtration property of water-based drilling fluid in unconventional reservoir and mechanism disclosure.

The research objective of this investigation is to explore the influence of filtrate reducer and reservoir characteristics on the filtration reduction of drilling fluid during the drilling process, and the filtration reduction mechanism of drilling fluids is also revealed. The results obtained that a synthetic filtrate reducer can significantly reduce the filtration coefficient than that of the commercial filtrate reducer. Moreover, the filtration coefficient of drilling fluid constructed from synthetic filtrate reducer is reduced from 4.9 × 10-2 m3·min1/2 to 2.4 × 10-2 m3·min1/2 with an increase in the filtrate reducer content, which is much lower than that of the commercial filtrate reducer. The weaker filtration capacity of the drilling fluid containing the modified filtrate reducer is attributed to the combined action of the filtrate reducer containing multifunctional groups adsorbed on the sand surface and the hydration membrane adsorbed on the sand surface. Furthermore, the increase in reservoir temperature and shear rate increases the filtration coefficient of drilling fluid, indicating that low temperature and shear rate are conducive to improve the filtration capacity. Thus, the type and content of filtrate reducer are preferred during drilling in oilfield reservoir, but increasing reservoir temperature and shear rate are not recommended. It is necessary to confect the drilling mud with appropriate filtrate reducer such as the chemicals prepared herein during drilling operation.

Influence of organoboron cross-linker and reservoir characteristics on filtration and reservoir residual of guar gum fracturing fluid in low-permeability shale gas reservoirs.

To effectively reduce the filtration rate of water-based fracturing fluid and promote the pressure holding effect of fracturing fluid in underground unconventional reservoirs, an efficient and clean organic-boron cross-linker was synthesized with boric acid and low alcohols. The results obtained that the synthesized organoboron cross-linker exhibits better fluid loss performance to water-based fracturing fluid than the commercially available cross-linker. This organoboron cross-linker allowed decreasing filtration coefficient more than 0.74 × 10-2 m3·min1/2 as a result of the network structure formed by the organoboron cross-linker and guar gum molecule. However, commercially available cross-linker exhibits a relatively large filtered mass of water more than 1.33 × 10-2 m3·min1/2 at the same condition. Meanwhile, the cross-linked guar gum fracturing fluid can significantly improve the fluid loss property with the increase of cross-linker content and pressure, and an increased fluid filtration gradually was revealed with increasing the reservoir temperature and current speed. Moreover, the damage of shale reservoir caused by the prepared boron cross-linker was only 11%, which was lower than 18% of the commercial boron cross-linker under the same conditions.

Experimental investigation on the high-pressure sand suspension and adsorption capacity of guar gum fracturing fluid in low-permeability shale reservoirs: factor analysis and mechanism disclosure.

Guar fracturing technology has been considered as a kind of popular EOR technology, but the weak static suspension capacity becomes a challenge due to the poor temperature resistance and stability of guar fracturing fluid. The main goal of this investigation is to explore the effect of different factors on the high-pressure static sand suspension of guar gum fracturing fluid by a synthetic efficient nano-ZrO2 cross-linker. In particular, a mechanism of static suspended sand of nano-ZrO2 cross-linker is analyzed by microscopic simulation. The adsorption performance of guar fracturing fluid on the shale surface is also studied for analyzing the environmental pollution and damage of guar gum fracturing fluid to shale reservoirs after cross-linking in this investigation. The results obtained that the inclusion of a small content of nano-ZrO2 cross-linker (0.4%) leads to an apparent increase of fracturing fluid viscosity and decrease in the falling quality of gravel (104 mPa·s and 0.3 g) compared to the classical cross-linker (63 mPa·s and 3.5 g). The lower adsorption capacity of guar fracturing fluid containing nano-ZrO2 cross-linker on the shale surface means that it has a weaker pollution ability to the shale reservoir than the commercially available cross-linker. Meanwhile, the grid structure density formed by nano-cross-linker and guar gum is considered to be the key factor to significantly change the suspended sand capacity. The investigation of nano-cross-linker cannot only provide necessary theoretical technology and data support for the stability of water-based fracturing fluid, efficient sand carrying, and the development of water-based fracturing technology, but also effectively protect the underground shale reservoir.

Affecting analysis of the rheological characteristic and reservoir damage of CO2 fracturing fluid in low permeability shale reservoir.

The fracturing property of liquid CO2 fracturing fluid varies greatly due to the rheology of fracturing fluid during fracturing process. The main objective of this investigation is to study the rheology property of thickened liquid CO2 by measuring the viscosity of thickened liquid CO2 in different physical parameters of this prepared thickener and explain the causes of rheological changes. The results show that thickener content, branching content, and molecular weight of a thickener for all could significantly improve the rheology of liquid CO2; the consistency coefficient K increased as they rose, but the rheological index n presented a decreased trend. Meanwhile, the mesh structure is proposed as a model to explain the rheological changes, and the large wetting angle means an excellent backflow, low reservoir damage, and low adsorption property. These results herein provide a basic reference to improve the CO2 fracturing technology and molecular design of CO2 thickener.