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Abstract In previous frac designs, proppant tracer logs revealed poor proppant distribution between clusters. In this study, various technologies were utilized to improve cluster efficiency, primarily focusing on selecting perforations in like-rock, adjusting perforation designs and the use of diverters. Effectiveness of the changes were analyzed using proppant tracer. This study consisted of a group of four wells completed sequentially. Sections of each well were divided into completion design groups characterized by different perforating methodologies. Perforation placement was primarily driven by RockMSE (Mechanical Specific Energy), a calculation derived from drilling data that relates to a rock's compressive strength. Additionally, the RockMSE values were compared alongside three different datasets: gamma ray collected while drilling, a calculation of stresses from accelerometer data placed at the bit, and Pulsed Neutron Cross Dipole Sonic log data. The results of this study showed strong indications that fluid flow is greatly affected by rock strength as mapped with the RockMSE, with fluid preferentially entering areas with low RockMSE. It was found that placing clusters in similar rock types yielded an improved fluid distribution. Additional improved fluid distribution was observed by adjusting hole diameter, number of perforations and pump rate.
An understanding of rock strength is important for designing recovery plans for a reservoir and for developing an appropriate reservoir simulation. A detailed discussion of rock failure can be found in Rock failure relationships and Compressive strength of rocks. But the data needed for these methods may not be readily available, so there is a desire to use data available from well logs that are available. Several techniques have been proposed for deriving rock strength from well log parameters. Coates and Denoo calculated stresses induced around a borehole and estimated failure from assumed linear envelopes with strength parameters derived from shear and compressional velocities.
In the process of analyzing treatment responses that occur during hydraulic fracturing, several variances in treating pressure exist that are not readily explained by examining the surface pressures and pipe friction in isolation. These variances are also apparent when looking at bottomhole injectivity. This paper demonstrates how engineers can take advantage of their most-detailed completions and geomechanical data by identifying trends arising from past detailed treatment analyses. The Eagle Ford Shale was deposited in the Late Cretaceous Period in a marginal to open marine setting. The Lower Cretaceous part can be divided into two second-order transgressive/regressive cycles that have been labeled lower and upper Eagle Ford. The deposition of these units varies across the formation as a result of topography at the time of deposition.
This page provides an overview of Pulsed-Neutron-Lifetime (PNL) devices and their applications. They probe the formation with neutrons but detect gamma rays. Chlorine has a particularly large capture cross section for thermal neutrons. If the chlorine in the formation brine dominates the total neutron capture losses, a neutron-lifetime log will track chlorine concentration and, thus, the bulk volume of water in the formation. For constant porosity, the log will track water saturation, Sw.
Density logging is another application of gamma rays in gathering data about subsurface formations. Density logging tools rely on gamma-gamma scattering or on photoelectric (PE) absorption. A density-logging tool sends gamma rays into a formation and detects those that are scattered back. Typical logging sondes use a Cesium-137 source, which emits gamma rays of 0.66MeV. At this high energy level, Compton scattering dominates.
The radioactivity of rocks has been used for many years to help derive lithologies. Natural occurring radioactive materials (NORM) include the elements uranium, thorium, potassium, radium, and radon, along with the minerals that contain them. There is usually no fundamental connection between different rock types and measured gamma ray intensity, but there exists a strong general correlation between the radioactive isotope content and mineralogy. Logging tools have been developed to read the gamma rays emitted by these elements and interpret lithology from the information collected. Conceptually, the simplest tools are the passive gamma ray devices. There is no source to deal with and generally only one detector. They range from simple gross gamma ray counters used for shale and bed-boundary delineation to spectral devices used in clay typing and geochemical logging. In Figure 1, the distributions of radiation levels observed by Russell are plotted for numerous rock types. Evaporites (NaCl salt, anhydrites) and coals typically have low levels. In other rocks, the general trend toward higher radioactivity with increased shale content is apparent. At the high radioactivity extreme are organic-rich shales and potash (KCl).
The first multilateral well in a North Kuwait field has been drilled recently. The intent is to improve oil production in productive layers subjected to water-coning problems by increasing reservoir exposure with Level-4 multilateral technology. The drilling process used a full suite of logging-while-drilling (LWD) tools, including azimuthal-deep-resistivity (ADR) technologies, to ensure the well path is precisely geosteered within the reservoir boundaries, and density/porosity tools in real time combined with specialized modeling software, to position the well in the best possible reservoir. Drilling horizontal wells aggressively primarily using inflow-control-device (ICD) completion techniques has been prevalent in North Kuwait fields. Although some multilateral wells had been drilled in other areas, the technology had not yet been adopted in these fields.
Many methods of calculating water saturation require knowing the chloride concentration in formation water. Chlorides have a strong effect on water properties, and they impact saturation estimates that are based on resistivity, dielectric dispersion, or thermal neutron absorption. Here we introduce a new direct quantitative measurement of formation chlorine from nuclear spectroscopy, enabling a continuous log of water salinity within a limited radial depth.
Neutron capture spectroscopy is sensitive to chlorine and is a natural fit for measuring its concentration, except that the spectrum contains chlorine from both the formation and borehole. The borehole chlorine background can be large and is highly variable. Historical efforts to derive water salinity from spectroscopy have relied on ratios of chlorine and hydrogen, which are affected by the borehole and hydrocarbons. The direct use of chlorine provides a more reliable basis for salinity interpretation after isolating its formation signal. We partition the borehole and formation components of chlorine via two unique spectral standards. The contrast between the two standards arises from differences in gamma ray scattering based on their point of origin. The shape of the borehole chlorine standard must be adjusted along depth to account for environmentally dependent scattering, which we achieve with a continuously varying function of borehole and formation properties. The algorithm is derived from 129 laboratory measurements and 2,995 numerical simulations spanning a diverse range of conditions. The remaining signal is converted into a log of formation chlorine concentration.
In combination with total porosity, chlorine concentration sets a minimum value for water salinity. Adding an organic carbon measurement enables the simultaneous estimation of water volume and salinity. Chlorine concentration can also be combined with a selected water salinity to compute a water volume for comparison with other methods. Finally, chlorine concentration enables calculation of a maximum expected sigma, which can identify the presence of excess thermal absorbers in the matrix.
The systematic uncertainty on the chlorine concentration ranges from 0.03 to 0.07 wt%, depending on borehole size. The resulting salinity accuracy is inversely proportional to porosity. A potential limitation of the measurement is its depth of investigation, reaching 8 to 10 in. for 90% of the signal. The chlorine concentration is sensitive to filtrate or connate water, depending on formation permeability and invading fluids.
We first present the technique to measure formation chlorine, supported by modeling, laboratory data, and core-log comparisons. We then propose petrophysical workflows to interpret the chlorine concentration.
This paper provides a history of nuclear spectroscopy in well logging from its beginnings in 1939 up until the present day. After the invention and implementation of gamma ray logging, this paper traces the technological development of the pulsed-neutron capture (sigma) log, the spectral gamma ray log, the carbon-oxygen log, tracer identification logs, small-diameter reservoir characterization tools, and finally the geochemical log.
The key to the science of nuclear spectroscopy has been the detection of gamma rays, their energies, and the identity of their parent atomic nuclei. From this, the properties of the formation can be better understood. There have been many advances in technology that have led to the current state of nuclear spectroscopy tools. The most notable has been the ability to detect the presence of a gamma ray. After this came numerous advances in scintillator crystal detector technology, the pulsed-neutron generator, the energy digitization of gamma ray pulses, fast-timing electronics, and powerful computers. These advances have made possible the complex, gamma ray-centric logging tools that we have today that have helped petroleum engineers in the energy industry locate and produce hydrocarbon, kerogen, and natural gas reservoirs for the benefit of each individual in the world. This paper discusses the rich history of these historic developments.
Abstract Objective/Scope: Advanced geo-navigation technique in multilateral wells is currently being used to optimize oil production from a number of reservoir zones in Mauddud formation in the ongoing development of Sabriyah oil field. Multilateral wells generally help reduce cost of hydrocarbon production and are known to perform better than single horizontal wells. However, the application of appropriate geo-navigation strategy and downhole logging-while-drilling (LWD) technologies to achieving maximum reservoir exposure is key to production outcomes. Well-ML was planned as a multilateral well with two horizontal drain sections LAT-0 and LAT-1, each targeting multiple reservoir zones MaB, MaC and MaD in Mauddud. The main objectives of the two horizontals was to place the wellbores in the more porous and less dense sections of the targeted reservoir zones, achieving 30 - 45%, 10 -15% and 50 - 60% of reservoir footages in MaB, MaC and MaD respectively. The variation in the reservoir depositional facies and structural uncertainties due to the presence of a major fault pose geosteering challenges, also risking not achieving the require reservoir footages in the targeted Mauddud reservoir zones. Methods, Procedures, Process: A geo-navigation model was created using offset well gamma ray, resistivity, bulk density and neutron measurements. Petrophysical evaluation of simulated curves from LWD tool responses along the wellbore trajectory was used to optimize the location of the horizontal wells in the targeted reservoir zones. Selection of BHA tool was based on the degree to which simulated curves from specific LWD tools displayed identifiable response to variation in reservoir facies and structural character. The implemented BHA comprised of the rotary steerable system, azimuthal deep resistivity "distance-to-boundary" technology, and the near bit density-porosity. Results, Observations, Conclusions: The enhanced geo-navigation technique of integrating the near-bit-density-porosity and the azimuthal deep resistivity distance-to-boundary tools played a major role in navigating the wellbore within the sweetest spot of the multiple reservoir zones with confidence. Percentage footage achieved in MaB-MaC-MaD was 49%- 14%-37% in LAT-0 and 34%-17%-49% in LAT-1. The positioning of the density/porosity sensors close to the drill bit reduced the reaction time to mitigate the challenges posed by abrupt changes in reservoir density/porosity characters and allowed for an earlier estimation of reservoir structural dips, particularly in MaC zone where there was poor azimuthal sensitivity in the deep resistivity measurements. The successful and continuous real-time geo-navigation operation resulted in an optimized production outcome that is 3 times the production from single horizontal producer recorded in the same multiple reservoir zones. Novel/Additive Information: Enhanced geo-navigation technique in multilateral well targeting multiple reservoir zones.