RESUMEN
Offshore drilling operations consist of complex and high-risk processes. Lack of situational awareness in drilling operations has become an important human factor issue that causes safety accidents. Prolonged work shifts and fatigue are some of the crucial issues that impact performance. Eye tracking technology can be used to distinguish the degree of awareness or alertness of participants that might be related to fatigue or onsite distractions. Oculomotor activity can be used to obtain visual cues that can quantify the drilling operators' situational awareness that might enable us to develop warning alarms to alert the driller. Such systems can help reduce accidents and save non-productive time. In this paper, eye movement char-acteristics were investigated to differentiate the situational awareness between a representa-tive expert and a group of novices using a scenario-based Virtual Reality Drilling Simulator. Significant visual oculomotor activity differences were identified between the expert and the novices that indicate an eye-tracking based system can detect the distraction and alert-ness exhibited by the workers. Results show promise on developing a framework which implements a real-time eye tracking technology in various drilling operations at drilling rigs and Real Time Operation Centers to improve process safety.
RESUMEN
Cement sheath is considered an important barrier throughout the life cycle of the well. The integrity of the cement sheath plays a vital role in maintaining the integrity of wells. Cement's ability to seal the annular space or a wellbore, also known as cement sealability, is an important characteristic of the cement to maintain the well integrity. It is believed that placing cement in the annular space or wellbore can totally prevent any leakage; however, that is debatable. The reason why cement cannot completely prevent fluid leakage is that cement is considered as a porous medium, and also flaws in cement, such as microannuli, channels, and fractures, can develop within the cement sheath. Furthermore, the complexity of casing/cement and cement/formation interaction makes it very difficult to fully model the fluid migration. Hence, fluid can migrate between formations or to the surface. This article presents a numerical model for gas flow in cement sheath, including the microannulus flow. A parametric study of different variables and their effect on the leakage time is carried out, such as the microannulus gap size, cement matrix permeability, cement column length, and cement porosity. In addition, it presents leakage scenarios for different casing/liner overlap length with the existence of microannulus. The leakage scenarios revealed that the cement matrix permeability, microannulus gap size, and cement length can highly impact the leakage time; however, cement porosity has a minimal effect on the leakage time. In addition, modeling results revealed that the casing/liner overlap length should not be less than 300 ft, and the casing pressure duration should be beyond 30 min to detect any leak.
RESUMEN
Drilling fluid and filtrates invasion often alter the near-wellbore flow properties during overbalanced drilling. The utilization of polymeric gels to prevent drilling fluid loss reduces the risk of formation damage caused by this alteration. In this study, the internal and external filter cake evolution by polyacrylamide (PAM) cross-linked with polyethylenimine (PEI) was investigated. The analysis conducted in this study showed that the cross-linked polymer activates and forms a mature gel inside the formation's pores. Gel also formed a dense uniform structure on the rock's surface, preventing further fluid loss. A high sealing pressure of up to 1000 psi was achieved, allowing drilling to continue without the need for additional casing string to prevent lost circulation. Moreover, the PAM/PEI formula showed less invasion of filtrate and evolution of a thin shallow internal filter cake that penetrated less than half of the filter disk thickness. In comparison to the full invasion and particle depositions that occurred with the water-based mud (WBM), the PAM/PEI formula is expected to reduce the impact of lost circulation materials (LCMs) on formation damage.
RESUMEN
Excessive water production from natural gas reservoirs is a main challenge facing the industry nowadays. Polymeric gelants have been widely applied to seal the water production zones, leading to a more feasible production operation. Nevertheless, conventional treatments fail in reservoirs characterized with the presence of sour gases. In this paper, aluminum-based salts are investigated as potential replacement for the conventional chromium acetate as crosslinkers for polyacrylamide (PAM), where aluminum has the advantage of being more environment-friendly besides its abundance. The investigation covers the whole pH range and examines the rheological behavior of the mature gels in the temperature range between 25 and 100 °C. While chromium acetate was proven to be sensitive to the presence of sour gases, namely, CO2 and H2S, because of the inability to produce a stable gel at the acidic conditions, this paper presents aluminum-based crosslinkers that are more tolerable toward high acidity. Unlike the conventional crosslinkers, the gelation rate in aluminum acetate and aluminum aminoacetate systems was found to decrease with the increase in pH. Both the crosslinkers succeeded in producing a strong gel with a storage modulus of more than 2000 Pa. Moreover, this study relates the physical stability of the colloidal aluminum crosslinkers with the viscoelastic behavior of the mature gel. The results reveal that aluminum acetate, among the screened salts, has a controllable gelation time at pH conditions between 3.5 and 8.5 and is the most stable in the temperature range 25-100 °C. PAM/AlAc system has a gelation time of around 50 min at 75 °C making it suitable for near-wellbore treatments, while the gelation time increased to 80 min upon increasing the pH of the system from 4.1 to 4.6. Moreover, the system showed good stability in saline conditions with NaCl concentration of up to 50,000 ppm. Scanning electron microscopy of freeze-dried samples proved the uniform distribution of colloidal crosslinkers and showed sheets wrapping around the colloidal particles. The performance of the new crosslinker is compared with available commercial crosslinkers.