Selection of Profile Techniques Based on Well Conditions

Abstract

Abstract Interpretation of the information obtained front well profiles is not an exact science. Preliminary interpretation is subject to local conditions, experience and performance data. Profiles are valuable to supply information an completion and production efficiency, for control of injected water to obtain maximum flood sweep, to determine the efficiency of the mechanical conditions of the well and to determine the causes of unpredictable behavior of a well. Methods and tools are discussed in respect to each techniques's application to the well conditions and the information desired. Typical surveys show the capabilities and hole conditions that can contribute to interpretation errors. From this discussion, techniques on techniques can he selected to obtain the maximum information on each well. Introduction The knowledge of injected fluid movement in and adjacent to the borehole is an approach to determining reservoir behavior. Interpretation of these observations is not an exact science. There are many known parameters that apply; but as with all types of surveys, many more must be assumed. Any preliminary interpretation is subject to alteration by local conditions and experience, prior or subsequent information from logs and performance data, etc. Useful and valid information can be obtained in both primary and secondary operations, however, by using the proper surveys and equipment for the information desired. Knowledge of both the response and limitations of various tools and techniques, and the effects of possible or probable downhole conditions are necessary to the correct choice. To obtain the desired flood sweep, the injection well conditions are of the utmost importance. Assumptions as to the mechanical conditions of the well can be misleading and result in wasted effort. The nature of waterflood operations creates many problems in that the wells are not new, records are sometimes inadequate, original completions are not efficient and equipment is worn. Injectivity profiles can provide a majority of the answers to a well's condition. Profiles are used to determine a wide variety of downhole conditions in both injection wells and producing wells in waterflood operations. A wide variety of tools and techniques are available to meet all well conditions. The two most commonly used are the tracejector with dual detectors and the packer spinner tool, supported by calipers and temperature tools as required (Fig. 1). Reasons for Profiles Confirm predicted performance or determine cause of unpredictable behavior by initial injection (or production) pattern; initial physical problems (thief zones, channels, parting planes, etc.); stabilized injection patterns; and developed or induced problems. Determine effective zone flooding by observing effects of pressure build-up, fill-up, flushing or top washing, vertical sweep, formation solubility or weathering and plugging. Assist in determining economic feasibility by indicating extent of preparation and/ or remedial work needed for effective operation; determining optimum rates and pressures needed; and observing formation characteristics under actual operation. Determine effectiveness of stimulation and corrective measures by comparison of performance results correlated to subsequent surveys. Methods and Tools Basic TracersRadioactive material is introduced into fluid stream at the surface or dumped in the hole above the zone with dump bailer and its path of travel and accumulation observed by successive logging runs over the zone of interest (Fig. 2). Qualitative evaluation is derived from the points of accumulation as indicated by gamma log. Very little control can be exerted once the material is placed, and considerable masking of true information can result from screening, spreading and fall-out. This is recommended for frac tracer (sand or resins) and zones of extremely high permeability or porosity. JPT P. 576ˆ