A novel responsive stabilizing Janus nanosilica as a nanoplugging agent in water-based drilling fluids for exploiting hostile shale environments

Thermo-responsive nanocomposites have recently emerged as potential nanoplugging agents for shale stabilization in high-temperature water-based drilling fluids(WBDFs). However, their inhibitory properties have not been very effective in high-temperature drilling operations. Thermo-responsive Janus nanocomposites are expected to strongly interact with clay particles from the inward hemisphere of nanomaterials, which drive the establishment of a tighter hydrophobic membrane over the shale surface at the outward hemisphere under geothermal conditions for shale stabilization. This work combines the synergistic benefits of thermo-responsive and zwitterionic nanomaterials to synchronously enhance the chemical inhibitions and plugging performances in shale under harsh conditions. A novel thermoresponsive Janus nanosilica(TRJS) exhibiting zwitterionic character was synthesized, characterized,and assessed as shale stabilizer for WBDFs at high temperatures. Compared to pristine nanosilica(Si NP)and symmetrical thermo-responsive nanosilica(TRS), TRJS exhibited anti-polyelectrolyte behaviour, in which electrolyte ions screened the electrostatic attraction between the charged particles, potentially stabilizing nanomaterial in hostile shaly environments(i.e., up to saturated brine or API brine). Macroscopically, TRJS exhibited higher chemical inhibition than Si NP and TRS in brine, prompting a better capability to control pressure penetration. TRJS adsorbed onto the clay surface via chemisorption and hydrogen bonding, and the interactions became substantial in brine, according to the results of electrophoretic mobility, surface wettability, and X-ray diffraction. Thus, contributing to the firm trapping of TRJS into the nanopore structure of the shale, triggering the formation of a tight hydrophobic membrane over the shale surface from the outward hemisphere. The addition of TRJS into WBDF had no deleterious effect on fluid properties after hot-treatment at 190℃, implying that TRJS could find potential use as a shale stabilizer in WBDFs in hostile environments.

Frictional stability of Longmaxi shale gouges and its implication for deep seismic potential in the southeastern Sichuan Basin

Microearthquakes accompanying shale gas recovery highlight the importance of exploring the frictional and stability properties of shale gouges.Aiming to reveal the influencing factors on fault stability,this paper explores the impact of mineral compositions,effective stress and temperature on the frictional stability of Longmaxi shale gouges in deep reservoirs located in the Luzhou area,southeastern Sichuan Basin.Eleven shear experiments were conducted to define the frictional strength and stability of five shale gouges.The specific experimental conditions were as follows:temperatures:90–270°C;a confining stress:95 MPa;and pore fluid pressures:25–55 MPa.The results show that all five shale gouges generally display high frictional strength with friction coefficients ranging from 0.60 to 0.70 at the aforementioned experiment condition of pressures,and temperatures.Frictional stability is significantly affected by temperature and mineral compositions,but is insensitive to variation in pore fluid pressures.Fault instability is enhanced at higher temperatures(especially at>200°C)and with higher tectosilicate/carbonate contents.The results demonstrate that the combined effect of mineral composition and temperature is particularly important for induced seismicity during hydraulic fracturing in deep shale reservoirs.

Mechanism of shales stabilization by hydrophobized poly(ethylene glycol)/K^(+) in water-base drilling fluids

The mechanism of the hydrophobized poly(ethylene glycol)(PEG)/K^(+) system inhibiting shale hydration was studied by laboratory experiment. The inhibition performance was evaluated through cuttings hot-rolling dispersion, bentonite inhibition and contact angle tests. The inhibition became stronger as contact angle and PEG concentration increased. A modified cuttings hot-rolling dispersion experiment suggested that these molecular systems did not act through the thermally activated mud emulsion(TAME) mechanism. The interaction of the PEG/K^(+) with clay samples was investigated through adsorption studies and by Fourier transform infrared spectroscopy(FT-IR), X-ray diffraction(XRD) and thermogravimetric analysis(TGA). The adsorption isotherms showed that the presence of K^(+) increased the PEG affinity for the clay surface. This inhibition effect was accompanied by a reduction of the bentonite hydration with PEG adsorption, evidenced by FT-IR, TGA and differential thermogravimetric(DTG) curves. XRD patterns were conclusive in showing that the presence of K^(+) ions limited the expansion of the clay interlamellar region to only one PEG layer, and the terminal hydrophobic segments of the PEG chains turned out to be determinant in enhancement of the inhibitory efficiency. The cuttings hot-rolling dispersion was carried out on water-base drilling fluid with PEG/K^(+), which proved the inhibition performance of PEG/K^(+) in oil field drilling.

Development and evaluation of an electropositive wellbore stabilizer with flexible adaptability for drilling strongly hydratable shales

In order to overcome serious instability prob- lems in hydratable shale formations, a novel electropositive wellbore stabilizer （EPWS） was prepared by a new approach. It has good colloidal stability, particle size dis- tribution, compatibility, sealing property, and flexible adaptability. A variety of methods including measurements of particle size, Zeta potential, colloidal stability, contact angle, shale stability index, shale dispersion, shale swelling, and plugging experiments were adopted to characterize the EPWS and evaluate its anti-sloughing capacity and flexible adaptability. Results show that the EPWS has advantages over the conventional wellbore stabilizer （ZX-3） in particle size distribution, colloidal stability, inhibition, compatibil- ity, and flexible adaptability. The EPWS with an average particle size of 507 nm and an average Zeta potential of 54 mV could be stable for 147 days and be compatible with salt tolerant or positive charged additives, and it also exhibited preferable anti-sloughing performance to hydrat- able shales at 77, 100, and 120 ~C, and better compatibility with sodium bentonite than ZX-3 and KC1. The EPWS can plug micro-fractures and pores by forming a tight external mud cake and an internal sealing belt to retard pressure transmission and prevent filtrate invasion, enhancing hydrophobicity of shale surfaces by adsorption to inhibithydration. The EPWS with flexible adaptability to tem- perature for inhibition and sealing capacity is available for long open-hole sections during drilling.

Shale hydration inhibition characteristics and mechanism of a new amine-based additive in water-based drilling fluids

In this work,shale hydration Inhibition performance of tallow amine ethoxylate as a shale stabilizer in water based drilling fluid,was investigated through these tests:bentonite hydration inhibition test,bentonite sedimentation test,drill cutting recovery test,dynamic linear swelling test,wettability test,isothermal water adsorption test,and zeta potential test.The results showed that bentonite particles are not capable of being hydrated or dispersed in the mediums containing tallow amine ethoxylate;tallow amine ethoxylate had shown a comparable and competitive inhibition performance with potassium chloride as a common shale stabilizer in drilling industry.Some amine functional groups exist in tallow amine ethoxylate structure which are capable of forming hydrogen bonding with surfaces of bentonite particles.This phenomenon decreased the water adsorption on bentonite particles'surfaces which results in reduction of swelling.Tallow amine ethoxylate is also compatible with other common drilling fluid additives.