Shubham, Agrawal (Texas A&M University at Qatar) | Martavaltzi, Christina (Texas A&M University at Qatar) | Dakik, Ahmad Rafic (Texas A&M University at Qatar) | Gupta, Anuj (Texas A&M University at Qatar)
It is well known that the majority of carbonate reservoirs are neutral to oil-wet. This leads to much lower oil recovery during waterflooding since there is no spontaneous imbibition of water in heterogeneous reservoir displacement. It has been verified by a number of researchers that Adjustment of ion concentration in brine solutions, or adding surfactant solutions can enhance the oil recovery by altering the wettability. In the published literature, contact angle studies usually refer to measurement on calcite crystals and there are no results for the contact angle of carbonate porous media representative of reservoir rocks. Moreover, there are few studies on the effect of non-ionic surfactants, compared to those for ionic surfactants. Understanding the effect of various ions and their concentration in the injection brine on the wettability of the Limestone outcrop core samples is the first step for tailoring of the optimum injection brine. This will be followed by a study of the effect of surfactant on the wettability of calcite crystal samples. The evaluation of the results may provide guidelines for the design of injection brines for efficient enhanced oil recovery from carbonate reservoirs.
In this work, a procedure is established for the measurement of the contact angle on limestone outcrop core samples. Results showed that, at atmospheric conditions, low salinity CaCl2 solution induced the most significant improvement on the wettability of the outcrop sample. Moreover, among all the non-ionic surfactants studied, only the presence of the two first members of the 15S analogous series might lead to a slight decrease of the contact angle.
The significance of exploring deep and ultra-deep wells is increasing rapidly to meet the increased global demands on oil and gas. Drilling at such depth introduces a wide range of difficult challenges and issues. One of the challenges is the negative impact on the drilling fluids rheological properties when exposed to high pressure high temperature (HPHT) conditions and/or becoming contaminated with salts, which are common in deep drilling or in offshore operations.
The drilling engineer must have a good estimate for the values of rheological characteristics of a drilling fluid, such as viscosity, yield point and gel strength, and that is extremely important for a successful drilling operation. In this research work, experiments were conducted on water-based muds with different salinity contents, from ambient conditions up to very elevated pressures and temperatures.
In these experiments, water based drilling fluids containing different types of salt (NaCl and KCl) and at different concentrations were tested by a state-of-the-art high pressure high temperature viscometer. In this paper, the effect of different electrolysis (NaCl and KCl) at elevated pressures (up to 35,000 psi) and elevated temperatures (up to 450 ºF) on the viscosity of water based mud has been presented.
The high-profile blowout at Macondo well in the US Gulf of Mexico, brought the challenges and the risks of drilling into high-pressure, high-temperature (HPHT) fields increasingly into focus. Technology, HSE, new standards, such as new API procedures, and educating the crew seem to be vital in developing HPHT resources. High-pressure high-temperature fields broadly exist in Gulf of Mexico, North Sea, South East Asia, Africa, China and Middle East. Almost a quarter of HPHT operations worldwide is expected to happen in American continent and the majority of that solely in North America. Oil major companies have identified key challenges in HPHT development and production, and service providers have offered insights regarding current or planned technologies to meet these challenges. Drilling into some shale plays such as Haynesville or deep formations and producing oil and gas at HPHT condition, have been crucially challenging. Therefore, companies are compelled to meet or exceed a vast array of environmental, health and safety standards.
This paper, as a simplified summary of the current status of HPHT global market, clarifies the existing technological gaps in the field of HPHT drilling, cementing and completion. It also contains the necessary knowledge that every engineer or geoscientist might need to know about high pressure high temperature wells. This study, not only reviews the reports from the Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE) and important case studies of HPHT operations around the globe but also compiles the technical solutions to better maneuver in the HPHT market. Finally, the HPHT related priorities of National Energy Technology Laboratories (NETL), operated by the US Department of Energy (DOE), and DeepStar, as a strong mix of large and mid-size operators are investigated.
Crespo, Freddy E. (University of Oklahoma) | Ahmed, Ramadan Mohammed (University of Oklahoma) | Saasen, Arild (Det norske oljeselskap ASA) | Enfis, Majed (University of Oklahoma) | Amani, Mahmood (Texas A&M University at Qatar)
Surge and swab pressures have been known to cause formation fracture, lost circulation, and well-control problems. Accurate prediction of these pressures is crucially important in estimating the maximum tripping speeds to keep the wellbore pressure within specified limits of the pore and fracture pressures. It also plays a major role in running casings, particularly with narrow annular clearances. Existing surge/swab models are based on Bingham plastic (BP) and power-law (PL) fluid rheology models. However, in most cases, these models cannot adequately describe the flow behavior of drilling fluids. This paper presents a new steady-state model that can account for fluid and formation compressibility and pipe elasticity. For the closed-ended pipe, the model is cast into a simplified model to predict pressure surge in a more convenient way. The steady-state laminar-flow equation is solved for narrow slot geometry to approximate the flow in a concentric annulus with inner-pipe axial movement considering yield-PL (YPL) fluid. The YPL rheology model is usually preferred because it provides a better description of the flow behavior of most drilling fluids. The analytical solution yields accurate predictions, though not in convenient forms. Thus, a numerical scheme has been developed to obtain the solutions. After conducting an extensive parametric study, regression techniques were applied primarily to develop a simplified model (i.e., dimensionless correlation). The performance of the correlation has been tested by use of field and laboratory measurements. Comparisons of the model predictions with the measurements showed a satisfactory agreement. In most cases, the model makes better predictions in terms of closeness to the measurements because of the application of a more realistic rheology model. The correlation and model are useful for slimhole, deepwater, and extended-reach drilling applications.
The ability to communicate between downhole and surface instruments became a critical need as well operators monitor flow rate, temperature, and pressure data to facilitate well performance optimization and maintenance. The use of wire lines for communication between downhole and surface is common, but these installations present cost, maintenance, and reliability issues. Wireless communications technology using acoustic waves is an interesting alternative to these wired systems. While the acoustic technology offers great benefits, a clear understanding of its propagation aspects inside the wells is lacking.
A testbed was built to investigate the propagation of acoustic signals over production pipes. The testbed comprises an acoustic tool that transmits data to the well surface without cables, an internally-developed receiver unit, and five segments of 7 inch production tubing that form a pipe string. Acoustic waves propagate in this setup by vibrating the pipes' body, without interfering with the surrounding medium. Moreover, to study the effect of cemented pipes on wave propagation, the third pipe segment was encased in concrete. An impulse signal was fed to the acoustic tool, and channel impulse response readings were taken along the pipe string. The measurements were analyzed to understand the propagation aspects of acoustic waves.
This work shows that acoustic waves experience dispersion and frequency-dependent attenuation over the pipe string; the pipe string appears as a frequency selective channel. The concrete segment filters out a considerable amount of energy in the higher frequency band and introduces further attenuation and dispersion. Signal processing algorithms are proposed to reduce the distortion and dispersion introduced by the pipe string channel on the acoustic waves.
Technical contributions include: finding the impulse response of the channel along the pipe string, investigating the power delay profile, power spectral density, and signal-to-noise ratio measures, and studying the channel dispersion parameters.
Wireless communication is a discipline that has widespread applications in different industrial areas. Gas and oil industry is one of the recently growing areas for potential applications of wireless communications technologies. Such technologies can be used for addressing issues in exploration, drilling, and production stages and improving their performances. For instance, well performance and production efficiency can be enhanced by having a means to communicate between surface and downhole tools. Reading of typical well data like gas flow rate, pressure, and temperature is crucial to monitor the performance of the wells. Currently, this data are obtained using wired systems. However, cost and reliability of such wired systems are prominent concerns. Therefore, alternatively, the existing wired systems can be replaced with wireless communications systems to acquire the vital data without interrupting production. Using acoustic waves to carry vital data from the wellbore to the surface and vice versa through the production tubing is a promising method to achieve wireless downhole communications.
While using the acoustic waves to carry information inside the oil wells offers great benefits, this technology lacks a clear understanding of its propagation aspects inside the wells. This article describes a testbed that was designed to characterize the propagation aspects of acoustic waves over production pipes. A wireless communication system was built using an acoustic transmitter, five segments of 7 inch production pipes, and an acoustic receiver. Channel impulse response results are discussed in this article, including the effect of concrete on signal propagation. Moreover, this article investigates the large scale statistics associated with the channel impulse response measurements; these measures include power spectral density, signal-to-noise ratio, power delay profile, mean excess delay, root mean square delay spread, maximum excess delay, and coherence bandwidth.
Tremendous amounts of hydrocarbons are located in deeper formations. In deep formations we experience higher pressures and temperatures. Designing a proper drilling fluid that can tolerate such high-pressure, high-temperature (HP/HT) conditions is very challenging. This work is focused on investigating the rheological behavior of water-based drilling fluids with different properties at extremely high pressure and temperature conditions using a state-of-the-art viscometer capable of measuring drilling fluids properties up to 600°F and 40,000 psig. The results of this study show that the viscosity, yield point and gel strength decrease exponentially with increasing temperature until the mud samples fail. This behavior is the result of the thermal degradation of the solid, polymers, and other components of the mud samples. Increase in the distance between molecules due to high temperature will lower the resistance of the fluid to flow and, hence, its viscosity, yield point, and gel strength will reduce. Moreover, conducting this study led to the conclusion that viscosity, yield point, and gel strength increase linearly as the pressure increase. Pressure's effect on these parameters, however, is more apparent at lower temperatures. Ultimately, the study concluded that the mud samples that were used, which are standard industrial types, failed at a temperature of 250oF and that the combined effect of temperature and pressure on mud's rheology is complex.