This paper discusses the effectiveness of the third-generation (Gen3) Production Logging Tool (PLT) technology which incorporates the use of co-located digital sensors for simultaneous acquisition of flow data. Case studies are provided which demonstrate that this technology is a step-change in the application of digitalization to a down-hole sensor platform which provides the most accurate characterization of the flow condition at each depth surveyed. The resulting data allows for much improved processing which is also described. The probabilistic interpretive model used in the processing has been updated to incorporate this and future developments in PLT architecture. Planning, execution, and analysis of data for the wells is described in detail. Due to the significantly shorter configuration of Gen3 tools, safety at the wellsite is enhanced by allowing for a much-simplified surface rig-up. One well was logged in surface readout (SRO) mode while data in the other two were recorded in the downhole tool's memory for retrieval at the surface at the end of operations. This flexibility in logging modes optimizes operations by addressing the needs of the operation teams. Three Deepwater Gulf of Mexico producers logged with the Gen3 PLT are described. In each case, a clear path forward is provided for optimal management of the reservoirs through effective production management. The first generation (Gen1) of PLT provided a single discrete measurement for each sensor along the tool assembly's length, resulting in long tool assemblies and measurements taken at different points along the flow path. This approach had several drawbacks: long toolstrings, point sensors only provided a measurement at a single point in the cross-section of the flow, and measurements were not acquired simultaneously at each depth logged. The second generation (Gen2) of PLT was an improvement as sensors were arranged as an array enabling multiple measurements to be made at a single depth but were still long and not all were optimally arranged to capture data in the path of flow. The Gen3 PLT is one-tenth the length of the Gen1 versions and roughly one-third of the shortest Gen2 tools. Digitization allows for direct measurement of flow conditions and rapid interpretation of results. In multi-phase flow and deviated wells, the co-location of sensors in a spatial geometry provides the optimal information with which to create a fully accurate picture of the downhole flow.

The Pinedale anticline is located in the Green River Basin of Southwestern Wyoming, USA. The field is the largest tight gas discovery for the onshore region of the United States in the last twenty years (Robinson and Shanley 2004). Gas production is from very tight, stacked clastic reservoirs that are Upper Cretaceous in age, with productive intervals in excess of 6000 feet. The large productive intervals require multiple hydraulic fracture stages to complete. Time-lapsed production analyses are performed to optimize well spacing and to characterize the gas bearing reservoirs. Production logs are also run to determine the effectiveness of the hydraulic fracturing and to identify water entry points that may lead to premature completion failures. Typical wells produce relatively small amounts of water, usually less than 5 percent by volume. It is nearly impossible to detect such small watercuts with conventional methods of production analysis. However, a probabilistic production analysis method simultaneously modeling flowmeter and temperature can take advantage of the high contrast between the heat capacity of gas and water and therefore provide good estimates of the water and gas production profiles, even in small watercut wells. This paper describes the technique used to improve the production flow profiling, supporting its assertions with case study results. Introduction Productive intervals in the field are stacked-lenticular tight sands with porosity ranging from 6 to 12% and permeability in the submicrodarcy to 20 microdarcy range, with an average value of 4 microdarcies. Water saturations vary from 30 to 60%, with comparably low water production. Condensate ratio with an API gravity of 52 is 8 to 10 bbl/MMscf (Eberhard and Mullen 2003). Numerous faults exist in the region, adding to the complexity of the reservoirs and creating over pressured gas zones in wells whose nearby offsets encounter normally pressure zones at similar depths. Pore pressure variability with depth does not follow a linear pattern, with intervals in the normal range bounded by layers in the geopressured zones. For this reason, individual production intervals must be hydraulically fractured in isolation with other intervals to assure effective treatment. Such complexities in the fracturing methodologies require an effective method of assessing flow contribution, both by phase and flow rate, of each productive layer. Additionally, the method used to estimate layer properties in multi-layer low permeability gas reservoirs (Spivey 2006) requires that accurate flow contribution be measured for each productive layer. Since the method requires multiple measurements over time as an input to the history match, consistent measurements and production log analyses are an absolute necessity. The combination of accurate production logging analyses and layer property determination provides the reservoir and production engineering teams with much more precise data than surface production data alone, maximizing the effective management of resources. With the cost of proppant representing as much as 30% of total completion cost (Huckabee et al 2005), accurate production analysis of the fracturing effectiveness can enable significant cost savings. Production Logging Methodology A typical completion (figure 1) consists of up to 24 frac stages each of which may have six perforated intervals ranging from 2 to 6 feet in length. Perforating shot density is 3 shots per foot. A 7 inch protection casing is set 600 feet from TD, with 4 ½' casing set from TD to surface. Flow-through composite fracture plugs (Eberhard, et al 2003) are used to isolate hydraulic fracturing treatments, then drilled out prior to production.

While ultrasonic logging devices have been used in recent years to determine the likelihood that casing strings are unbonded and thus free to be removed in a casing recovery, this application is still under development. The uniqueness of this application lies in the fact that the bonding forces present on the outside of the casing are caused by drilling fluids in varying stages of decomposition as opposed to cement. The fact that the exact composition of these altered fluids is unknown makes it difficult to quantify their compressive strength, leaving no clear method for anticipating an acoustic response. Virtually all of the acoustic devices in use today, when used for any application other than borehole imaging, were developed to quantify the ability of cement in the casing-formation annulus to provide a pressure barrier between zones connected to one another by the wellbore. In every such case, the cement used to provide the isolation is of a known chemical composition and extensive laboratory experiments are conducted to precisely measure its compressive strength and other properties. Since there exists no such opportunity to measure the properties of the material in an uncemented annular space, theoretical solutions have been developed which estimate the extent of adhesion these materials cause. This paper discusses the applicability of such theoretical solutions and substantiates its conclusions with case studies. Introduction In order to sidetrack out of a previously completed well, it is generally necessary to remove one or more of the existing casing strings to gain access to a larger casing interval from which to kick the new well off. This allows for the use of a larger casing in the new well than could be placed were the internal casings not removed. In this case, the internal casing strings, while well cemented in their deeper intervals as required by sound well completion practices, are generally not cemented in their upper sections. The removal of the internal casings can be accomplished more efficiently if the precise point at which they are no longer held in place by adhering forces of the material surrounding them is known. While it is known that the adhering forces are caused by barite settling out of the drilling mud placed in the casing-to-casing annuli, acoustic information has been collected for homogenous mud, fluid, and cement samples only. (Table 1) Additionally, the information gathered is limited to acoustic impedance, which is not easily directly related to material strength, as can be seen by the tabulated values which show that impedance is more closely related to cement slurry density that it is to compressive strength.

New techniques for well abandonment log evaluations have been under study since 2012 in the Gulf of Mexico (GOM). Legacy practices typically used acoustic methods consisting of cement bond log and ultrasonic scanner devices. The new methods described in this paper consist of adding nuclear sensors to supplement the acoustic measurements and introduce novel processing methods. Behind pipe evaluation techniques (BPET) is the overall solutions package described within the paper. When properly modeled and analyzed, this data has the potential of significantly reducing the cost of removing casing strings during plug and abandon activities.A new development in CBL refracted waveform processing provides relative amplitude mapping within four concentric cylindrical volumes between the CBL transmitters and receivers. These regions extend from the first casing and its annular region and outwards within the wellbore. The density and neutron nuclear sensors allow grouping of detector count rate ratios in data clusters which have been interpreted to be responding to annulus materials spanning from cement, heavier liquids, settled mud solids, lighter liquids, and gas. Neutron responses are useful in trending the relative hydrogen index of the annular contents. Distribution imaging of settled solids from ultrasonic measurements have been helpful in supplementing the interpretation of nuclear and refracted waveform indications.More than 27 log runs were conducted with the applied abandonment evaluation methods in the deepwater sector of the GOM. One of the benefits derived from conducting the evaluations in abandonment operations is the ability to validate interpreted log predictions with additional surveys after the cut and extraction of primary casing strings. An interesting example from time-lapse surveys is included. Detection of hydrocarbon gas before release of the casing hanger and during circulation operations can reduce risks from a health, safety, and environment (HSE) perspective. Frequently, during the abandonment phase, casings can have accumulated mud solids on the exterior surface. This phenomenon can mask the detection of gas from shallow-reading ultrasonic measurements. The density and neutron nuclear sensors allow slightly deeper detection of annular material responses. Examples where gas was detected through casing and associated post-cut results are shared. Cut-and-pull rig tension prediction has been another deliverable developed from the described methods. Results from this technique are displayed along with available actual applied rig tensions during casing extractions. The paper describes current downhole logging tool configurations allowing variable depth of measurement and shares the interpretation methods practiced through well case history study examples.Although primary applications of the method were developed and applied for well abandonment purposes, other uses of the new technique could include sidetrack window positioning in wells without previous cement evaluation logs available over the targe...

Evaluation of cement placement is an important part of the majority of deepwater wells. Cement placement confirmation is an important step following a cementing operation. More than one technique can be used to provide information about the top of cement (TOC) and about the depth interval of a good bond between the formation and the casing. Determining the length of annular cement coverage, which is an indication of correct cement placement, is useful knowledge before drilling and/or completion operations can proceed. The requirement for additional and improved cement evaluation techniques is greater now than ever before. A variety of methods can be used to evaluate cement placement. The routine approach after a casing or liner cement job uses a job chart to calculate lift pressure and actual vs. predicted system pressure. These data enable an estimate of cement height in the annulus to be made, but they do not confirm the TOC. These methods vary in accuracy and difficulty, depending on well conditions. Common TOC evaluation methods in specific wellbore casing/liner sections typically require running a temperature survey or cement bond log (CBL) sensors/systems on a wireline. These operations use the rig's critical path time for each wireline run, which can add risk or difficulties, depending on the well trajectory. In addition, cement bond evaluation for large diameter casing can be technically challenging because it can reach the upper threshold measurement limitations for conventional wireline-conveyed CBL tools. Many operators now use logging-while-drilling (LWD) sonic sensors for compressional and shear data acquisition in openhole environments. Using the same sonic systems, with minimal additional rig time, logging data acquired through the casing/liner strings while running a drilling or clean out assembly can be evaluated to confirm the TOC. This paper demonstrates how LWD sonic technology can provide confirmation of the TOC, saving a considerable amount of rig time, as compared to performing a dedicated wireline evaluation run or potentially unnecessary cement squeeze operations. The paper presents and discusses Gulf of Mexico (GOM) case studies. Based on various specific challenges, through correct data analysis, TOC evaluation best practices are implemented to optimize the LWD acoustic data acquisition inside the casing/liner. New data examination techniques are reviewed that can be applied to different scenarios, such as TOC evaluation behind dual pipes and real-time assessment for quick data analysis turn-around. In conjunction with the case studies, the paper also provides information about the LWD cased-hole logging techniques, analysis, and results of the data application.