Nonreflection seismic and inversion of surface and guided waves 936 The Leading Edge June 2013 Nonreflection seismic and inversion of surface and guided waves Field testing of fiber-optic distributed acoustic sensing (DAS) for subsurface seismic monitoring
Potential mechanisms involved in microbial enhanced oil recovery (MEOR) from sandstone reservoirs are reviewed. Three phase relative permeability studies have shown that residual oil saturation can be reduced by the presence of gas in a water wet system. The production of biogenic gas to create a free gas phase can account for incremental oil recovery in MEOR processes. Reduction in interfacial tension between formation fluids can be caused by metabolic products. Also, bacterial plugging appears to preferentially occur in larger, high plugging appears to preferentially occur in larger, high permeability pores. As this occurs fluid is diverted into smaller pores permeability pores. As this occurs fluid is diverted into smaller pores causing an increase in fluid velocity within them. The changes in interfacial tension and fluid velocity combine to increase capillary number. Increases in capillary number are associated with reduction of residual oil saturation. Core experiments are related to the results of these studies. The methods discussed can partially account for additional oil recovery in an MEOR process. Introduction For the development of microbially enhanced oil recovery (MEOR) as a viable technology in the petroleum industry, it is important that the mechanisms involved in this process be understood. MEOR has the potential to recover a portion of the residual oil remaining after waterflooding portion of the residual oil remaining after waterflooding through changes brought about by metabolic activity. The changes include selective plugging of the reservoir and modification of the reservoir fluids and their saturations. This paper will address primarily the latter two of these. The goal of the authors is to expand the current body of knowledge on the microbial mechanisms involved in the MEOR process. However, the mechanisms discussed herein cannot account for all of the oil that has been produced from core experiments. EXPERIMENTS The experiments reported in this paper were conducted to provide information about the mechanisms of oil recovery caused by microbial activity within a core. Specifically, samples of microorganisms from well 1A-9 in the Southeast Vassar Vertz Sand Unit (SEVVSU), Payne County, Oklahoma were investigated for their potential in microbial enhancement of oil recovery. All experiments were performed using oil and brine taken from the SEVVSU. The NaCl salinity of the brine was 15%. The experiments were performed at reservoir temperature using the apparatus in Figure 1. The cores were prepared and experiments conducted using the techniques of prepared and experiments conducted using the techniques of Silfanus and Knapp, et al. The experiments were performed using the three step treatments described below. performed using the three step treatments described below. Consider an MEOR core flood with apparatus as shown in Figure 1. In this experiment a core is cleaned, dried, and flushed with brine, oil, and brine again, such that the final condition is a water wet core at residual oil saturation. The MEOR experiment is begun by an injection of nutrient rich brine containing bacteria. The experiment proceeds with three steps per treatment. First, the core is shut in and allowed to incubate. Second, the effluent end of the core is opened and fluids are produced under the influence of any internal driving force. Third, the core is flooded and fluids are produced under the influence of the flood. The displacing liquid is a nutrient rich brine which represents the carbon source for the next incubation. These three steps are repeated for each treatment. The effective permeability reduction factor (PRF) is defined as: ........................................(1) Petroleum Engineers processes, a series of nutrient treatments are used to Petroleum Engineers processes, a series of nutrient treatments are used to improve oil recovery. The incremental oil recovery associated with each nutrient treatment is the oil produced by the release of pressure caused by the in situ gas produced during incubation of the core with nutrients plus the oil that is produced by the injection of the subsequent treatment. P. 169
The management of directionally drilled wells has recently progressed to the stage where targets have been reduced in size to a point in the earth with no tolerances. These targets can and are changed during the drilling process. The management of these point moving targets, usually in high angle or horizontal wells, is a predse form of directional drilling now called geosteering. It is this predse placement of the wellbore that creates the value in drilling these wells.Sever~ technolo~es have made this advancement possible. These mclude rehable steerable systems, improved and new physical formation measurements, log data modeling, sensors near the bit and instrumented motors, and detailed reserYoir mapping with the help of 3D seismic processing. ~lost papers on geosteering have concentrated on one of these advances. This paper addresses how these technologies are merged to execute the successful geosteering project.New systems, sensors, and computations have created a m~s. of data and control parameters that require real-time deCisions by operator persom1el based on technical recommendations from service companies. These decisions have ~ critical impact on the net worth of a project. The team mvolved must rely on each other's expertise and under~tan~ t~e overall objective of a geosteering project. To do this, lt 1s paramount that data from these different technological areas be merged into a 3D visualization encompassing geological stn1ctures and drilling trajectories.Patterns in procedures have developed from these projects over the past three years which demonstrate the difference b~tween a ~uccessful project and a failure. 1he examples in this paper Illustrate the techniques that will enable a change 133 in the outlook towards precision directional drilling and completion projects.
Increasing water depth, total well depth, synthetic mud systems and increasing measurement complexity pose unique challenges for real-time data transmission via mud pulse telemetry. In deepwater environments, where the use of synthetic oil-based mud is prevalent, low water temperature significantly increases mud viscosity which reduces the signal strength at surface and makes detection of the signal more difficult. Noise within the mud channel further hinders transmission of downhole data. With rig rates approaching $350k per day and total well depths beginning to exceed 10700 m (35,000 ft), operators cannot afford to drill ahead without good quality real-time downhole data. On recent wells in deep water conditions in the Gulf of Mexico as many as seven different measurement while drilling/logging while drilling (MWD/LWD) tools have been run concurrently. Some of these tools may include the capability to produce real-time images. There is thus an increasing demand for higher data rates coupled with more reliable telemetry to transmit all this data to the surface in real-time. Recent advances in MWD tool design, signal strength prediction, and signal recovery on the surface, using advanced digital signal processing techniques, have made it possible to double telemetry data rates while also reducing error rates in the data received at the surface. Introduction Real-time transmission of data from sensors located downhole near the drill bit is a critical factor in safely and cost efficiently drilling wells that will maximize production from hydrocarbon reservoirs in the earth. Data from downhole sensors fall into two main categories: drilling data and formation evaluation data. The drilling data provide information for measuring and steering the trajectory of the well, such as survey data with the direction and inclination (D&I) of the drill bit and tool face orientation. Other important drilling data may include conditions in the well such as annular pressure and downhole temperature. The tools used for measuring directional information and generating pressure wave signals are usually called measurement while drilling (MWD) tools. If "wireline quality" logs are required in real-time, one measurement needs to be made for every 150 mm (6-in.) of hole drilled. When a typical "triple combo" service is run, eight variables (data words), of approximately 10 bits each, are transmitted for each measurement interval. At a rate of penetration of 30 m/hour (100 ft/hour) this would require a data transmission rate of greater than 4.5 bits/s. In this paper, we present a brief introduction to the generation, transmission and reception of mud pulse signals. This includes descriptions of how the signals are generated and the mud channel characteristics, such as attenuation and noise problems. We then discuss solutions available today to maximize the throughput and quality of real-time data transmitted from downhole MWD and LWD tools, especially in the context of drilling wells in deepwater applications and in wells that may have total lengths exceeding 10 700m (35,000 ft). Mud Pulse Telemetry Systems Mud pulse telemetry is still the most widely used and reliable method for transmitting data from downhole sensors to the surface while drilling. The concept of mud pulse telemetry for measurement while drilling applications is not new. Arps and Arps1 in 1964 described an early MWD system that used a plunger valve for generating discrete mud pulses. Data rates of less than 1 bit/s can be achieved using this type of modulator. Patton et al.2 in 1977 described a Mobil MWD system that used a rotating valve mechanism (also known as a mud siren) to generate continuous-wave telemetry using phase shift keying modulation. Data rates of up to 3 bits/s were claimed in the article.
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