Search

During the process of hydrate reservoir drilling, the heat generated by friction in a horizontal well section leads to hydrate decomposition and affects the wellbore stability. Consequently, the low-temperature environment of subsea wellbores can cause hydrate regeneration and flow obstacles. In this study, modified n-alkanes (MNA) with an appropriate phase transition temperature and acceptable latent heat were synthesised, and the thermal conductivity was improved by adding nano-Cu. A composite phase change material (PCM) was prepared using expanded graphite (EG) with adsorbing MNA, and nano-silica modification to improve its hydrophilicity and stability. Structural properties of the composite PCM were characterised via scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, and nitrogen sorption. The DSC curves revealed an acceptable latent heat capacity and reliability of the prepared composite PCM. In addition, by simulating the temperature heating and cooling during the drilling process, the composite PCM exhibited a reasonable thermoregulating and hydrate decomposition inhibition performance, which can effectively inhibit hydrate decomposition in reservoirs and hydrate regeneration in wellbores. Moreover, the composite PCM exhibited a reasonable compatibility with the drilling fluid. The study results can be applied to realise intelligent temperature control and reduce the risk of drilling in hydrate reservoirs.

The friction heat generated during the drilling process of natural gas hydrate bearing sediment (HBS) leads to the temperature of drilling fluid higher than the phase equilibrium temperature of hydrate, which induces hydrate decomposition and wellbore instability. In this work, tetrabutylammonium bromide (TBAB) and Nano-silica were microencapsulated by inverse emulsion interfacial polymerization. The effect of different preparation conditions on the encapsulation rate of microcapsules was characterized by differential scanning calorimetry (DSC), and the highest encapsulation rate was 62.2% with the melting enthalpy of 121.4 J/g. Polarizing microscope, scanning electron microscope (SEM) and transmission electron microscope (TEM) images were used to characterize the synthesis process and microstructure of microcapsules, which proved a quasi-spherical structure coated with Nano-silica. Furthermore, it was confirmed that the microcapsules also had good thermal conductivity, reliability and thermoregulating performance. The rheological parameters of drilling fluid with 5 wt% microcapsules increased slightly, and the filtration loss decreased, indicating good compatibility. In addition, it is convenient to adjust the melting temperature of the core materials by adding NaCl with different concentrations. This study is of guiding significance to realize intelligent temperature-control of hydrate bearing sediment during drilling.

Inhibiting hydrate decomposition due to the friction heat generated by the drilling tools is one of the key factors for drilling hydrate formation. Since the existing method based on chemical inhibition technology can only delay the hydrate decomposition rate, a phase-change microcapsule was introduced in this paper to inhibit, by the intelligent control of the drilling fluid temperature, the decomposition of the formation hydrate, which was microencapsulated by modified n-alkane as the core material, and nano-silica was taken as the shell material. Scanning electron microscope (SEM), size distribution, X-ray diffraction (XRD), and Fourier transform infrared spectrometer (FT-IR) were utilized to characterize the structural properties of microcapsules. Differential scanning calorimetry (DSC) spectra displayed that the latent heat was 136.8 J/g in the case of melting enthalpy and 136.4 J/g in the case of solidification enthalpy, with an encapsulation efficiency of 62.6%. In addition, the prepared microcapsules also showed good thermal conductivity and reliability. By comparison, it was also proved that the microcapsules had good compatibility with drilling fluid, which can effectively control the temperature of drilling fluid for the inhibition of hydrate decomposition.

Drilling fluid in Arctic permafrost needs to have good ultra-low temperature rheology, shale inhibition, hydrate inhibition and environmental protection performance. In this work, the properties of ultra-low temperature drilling fluid and additives have been evaluated by using rheology and fluid filtration tests, shale inhibition tests, hydrate inhibition tests, thermal conductivity measurements and biotoxicity tests. Thereafter, the key additives have been optimized and the ultra-low temperature water-based drilling fluid formula was developed. The results show that the base fluid, which combined NaCl and ethylene glycol (EG), can meet the requirement of freezing point in Arctic drilling, and it also has low thermal conductivity and good hydrate inhibition. Xanthan gum (XC) and hydroxyethyl cellulose (HEC) have been selected as viscosifiers, carboxymethyl starch (CMS) as filtrate reducer and polyetheramine as shale inhibitor. The drilling fluid has good ultra-low temperature rheology with the freezing point of −32 °C. Furthermore, it has low thermal conductivity, and can inhibit shale dispersion, expansion and collapse, which is conducive to the stability of wellbore in Arctic permafrost. In addition, it can effectively inhibit hydrate formation and has good environmental protection performance. The drilling fluid invented in this study can provide technical support for ultra-low temperature drilling in Arctic permafrost.

To balance conflicts for high-resolution, large-field-of-view and real-time imaging, a retina-like imaging method based on time-of flight (TOF) is proposed. Mathematical models of 3D imaging based on MOEMS are developed. Based on this method, we perform simulations of retina-like scanning properties, including compression of redundant information and rotation and scaling invariance. To validate the theory, we develop a prototype and conduct relevant experiments. The preliminary results agree well with the simulations.

A three-dimensional (3D) laser imaging system based on time of flight is proposed, based on the human retina structure. The system obtains 3D images with space-variant resolution, and we further establish mathematical models of the system and carried out simulative comparison between space-variant structure (SVS) and space-invariant structure (SIS). The system based on SVS produces significant improvements over traditional system based on SIS in the following aspects: (1) The system based on SVS uses less pixels than that based on SIS under the same field of view (FOV) and resolution. Therefore, this property is more suitable for uses in situations that require high speed and large volume data processing. (2) The system based on SVS has higher efficiency of utilization of photodiode array than that based on SIS. (3) 3D image based on SVS has the properties of rotation and scaling invariance. (4) The system based on SVS has higher echo power in outside ring of large photodiode array, which is more effective in detecting targets with low reflectance.

We propose a three-dimensional imaging system based on retina-like structure. The system has advantages of space-variant resolution, rotation and scaling invariance. Those properties are more suitable where requires high speed and large volume data processing.

A ranging method based on the differential time domain method (DTDM) is proposed in order to improve ranging accuracy and the range of active measurement based on peak discriminator (PD). We develop mathematical models and deduce that zero-crossing sensitivity is an important factor, which affects the ranging error of DTDM. Additionally, zero-crossing sensitivity is determined by delayed time. We carried out relative experiments and obtained the smallest ranging error when delayed time is receiving pulse width. We also compare ranging, three-dimensional (3D) point clouds and depth images based on two methods under same testing conditions. The results show that DTDM is beneficial in improving performance of pulse laser ranging and 3D imaging.