While traditional mudlogging techniques provide largely qualitative data, the prime objective of Advanced Mud Logging (AML) is to provide quantitative real time measurements in aid of a complete formation evaluation. To achieve this, wellsite mudlogging technologies have been enhanced, and various techniques which historically were limited to laboratories, have been adapted for well site usage. AML well site techniques thus include: (1) high frequency, improved accuracy monitoring of drilling parameters; (2) enhanced cuttings image acquisition and processing; (3) direct measurements on cuttings, including graindensity, spectral GR, NMR, XRD, XRF; and (4) sophisticated mud gas analysis capabilities.We describe the main system components developed and present some results of the first pilot tests done in Saudi Arabia with AML techniques and a dedicated AML unit. Examples in the four areas mentioned above illustrate and confirm the potential of AML. On one special technology test well, different systems, from two different companies, were run in parallel to establish the merits and possible limitations of especially the hydrocarbon analysis systems.One of the most striking examples of the quality of AML is a perfect match between the hydrocarbon fluid composition determined from mud gas returns, and those subsequently obtained from PVT measurements on wireline fluid samples. To achieve this, AML technology developers in the industry advanced across the whole process chain affecting such quantification. First and foremost, improving sample extraction and handling, combined with enhanced calibration procedures, to convert from in situ to surface conditions. Second, in addition to sampling both the return mud flow and the inflow, a more precise tracking of flowrates and system volumes was made possible with modern operating systems. Third, adding a mass spectrometer to the gas chromatograph, improved the final measurement potential. Introduction.Several years ago, in Saudi Aramco, a clear business need emerged for additional petrophysical techniques in cases where traditional formation evaluation technologies were unable to provide all the necessary answers with sufficient certainty. Interpretation of tight gas formations in particular was challenging, because the formation properties typically were right at the edges of the operating envelopes of normal logging tool measurements and interpretation technology. With a perceived potential for AML technologies to aid in several of those challenges, an AML research area was set up. The mission was to expand and improve existing mudlogging technologies, and introduce and develop new ones. The vision had two related, but distinct elements. Firstly, also labeled as "ARCHIE'S DREAM" 1 , a complete, albeit preliminary, as a "first aid", formation evaluation, based solely on AML data, including mineralogy, fluid contacts and fluid characterization, porosity and even saturation, permeability and other parameters normally derived from conventional electric logging and cori...

Delineation of oil and water in heterogeneous carbonate formations can be challenging, especially in the presence of low resistivity formations and low mobility zones. Advanced wireline formation testers (WFTs) have traditionally been used in openhole logging for pressure profiles, coupled with downhole fluid analysis (DFA) and sampling for an integrated approach. It is often difficult to obtain well defined oil and water gradients with pressure measurements in tight formations, especially with probe-type tools. Straddle-packer modules are often used to enable flow from low mobility formations. However, the straddle-packer module has operational and differential pressure limitations, as well as a relatively large storage volume in the isolated interval. A field example of oil-water delineation is presented for a low resistivity, heterogeneous carbonate formation. Low formation fluid mobilities required the utilization of a new wireline tester module over the standard probe type tool. A newly designed fluid inlet module with multiple openings was utilized across the low mobility zones for the first time in the industry. This new module avoids issues associated with the interval volume of a dual-element straddle-packer-type tool and provides significantly faster clean up from the formation. In addition, minimized storage results in better Interval Pressure Transient Test data. Faster set/retract operation of this tool and a much higher pressure differential limit are additional advantages over existing dual packer tools. Several station measurements with mobilities of less than 0.1 md/cp were conducted. This allowed oil to be identified across a low resistivity zone, leading to an increased oil column height in the field. Results showed that more accurate oil-water delineation was provided using the new module along with high resolution optical fluid analyzers, identifying mobile oil from low resistivity carbonate zones. In addition, more accurate permeabilities for the tested zones were obtained through pressure transient data analysis.

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Saudi Aramco's first deepwater exploration well targeted a sub-salt Miocene syn-rift section located in over 2,000 ft of water and beneath 9,000 ft of halite and evaporites. Offset well information from previous shallow exploration wells was limited; therefore, calibration for pre-drill pore pressure and fracture gradient prediction (PPFG) was performed using a single shallow water well completed two months prior to spuding the well. Pre-drill PPFG predictions presented a very high degree of uncertainty, which translated into uncertainty in well design and mud weight planning. Pre-drill pore pressure prediction relied on seismic velocities extracted from a wide azimuth 3D survey and used Residual Normal Move Out (RNMO) and seismic inversion to extract velocities that were presumed to represent shale velocities. Real-time pore pressure monitoring was based on a comprehensive program that included logging while drilling (LWD), multiple look-ahead vertical seismic profiles (VSPs), velocity model updating and rapid remigration (pre-stack depth migration) around the wellbore to produce simultaneous improvements in imaging and depth estimates that were tied back to an evolving geological pore pressure model. Significant differences between the pre-drill pore pressure model and measured well pressures highlight the critical importance of the pre-stack depth migration (PSDM) velocity model and the necessity to be able to modify the seismic velocity model and calculated pore pressures in real time to provide accurate information to drilling operations. An integrated team of technical professionals from nine separate departments was required to successfully carry out this project, which resulted in the successful drilling of a deepwater well in a high overpressure -low fracture gradient environment with minimal operational downtime. Geological Setting and StratigraphyOpening of the Northern Red Sea rift began approximately 25 MaBP as the Arabian platform began to move east (25-15 MaBP) then northeast (15-0 MaBP) relative to the African craton. Initiation of the Northern Red Sea rift triggered the onset of syn-rift deposition into a series of graben and half graben basins that continues to present day. The deepwater (beyond 1,000 ft water depth) syn-rift stratigraphy consists of Oligo-Miocene sediments up to 21,000 ft thick deposited under varied depositional environments and settings that are related to the macro tectonic evolution of the rift system. In terms of

With the recent introduction of NMR Logging While Drilling tools and down-hole NMR Fluid Analyzers, the more fundamental T1 measurement has made its appearance in the oil patch. In both these applications, the preference of T1 over T2 has been its insensitivity to motion, since T1 measurements effectively eliminate the detrimental effects arising from tool motion or fluid flow. Experience has shown that the acquisition and interpretation of T1 logs recorded in the less hostile wireline environment is quite straightforward, mainly due to the absence of tool motion, while yielding several benefits over T2 logs. T1 is a critical fluid NMR parameter and can play a prominent role in fluid typing applications. Also, T1 data sets are more compact and the acquisition is more efficient. Finally, T1 logging offers the potential of substantially increased logging speeds. This paper outlines the current T1 logging practice, and substantiates the advantages of T1 logging using real-life data. Examples included demonstrate the value added by wireline T1 measurements into the overall petrophysical understanding of in-situ reservoir fluids. Introduction The spin-lattice (longitudinal) relaxation time T1 contains important surface and bulk relaxation information used in the determination of critical petrophysical answers such as irreducible water saturation, and hydrocarbon properties. In contrast to more popular T2, T1 is not affected by fluid diffusivity, internal gradients or instrumentation artifacts. Although much of the earlier petrophysical work was based on T1 measurements1,2,3, due to technical limitations4, T2 logging became the method of choice in the early nineties. The more fundamental T1 measurement has made its appearance in the industry with the recent introduction of NMR Logging While Drilling tools and down-hole NMR Fluid Analyzers5,6. With both these devices, the preference of T1 over T2 has been its insensitivity to motion, since T1 measurements effectively eliminate the detrimental effects arising from tool motion or fluid flow. Experience has shown that the acquisition and interpretation of T1 logs recorded in the less hostile wireline environment, where (lateral) tool motion is not an issue, is straightforward and even has some benefits over T2 logs. T1 logs provide the same critical NMR petrophysical information available from T2 logs, in terms of porosity, irreducible water saturation, and permeability. Furthermore, determination of the hydrocarbon type, or calculation of the flushed zone hydrocarbon saturation using T1 logs can be much simpler in certain applications. T1 logging also offers the potential of increased logging speeds, which could address a major stumbling block in the general acceptance of NMR logging as a routine application. These statements should not be interpreted to downplay the role of T2 logs; there are many synergies to be exploited between T1 and T2 logs, as demonstrated in the case study presented in the paper. The main objective of this paper is to document the feasibility of wireline T1 logging. Following brief discussions on the physics of the measurement and signal processing, a case study is used to demonstrate the value added by T1 logs. A second objective, once again using real data, is to prove that the quality of the answers, or the level of uncertainty in T1 logs, is at least as good as that of T2 logs. The T1 measurement The first and most fundamental step in any NMR measurement is to align the magnetic nuclei with a magnetic field. This alignment process, or polarization, is not instantaneous and takes some time. The time constant associated with it is called T1. In reservoir rocks, the value of the apparent (or measured) T1 depends strongly on the characteristics of the fluids and the confining pore space. Two distinct relaxation mechanisms acting in parallel determine the longitudinal relaxation time:Equation 1 Where the subscripts B and S correspond to bulk and surface relaxation, respectively.