Production of high salinity formation water with gas presents major operational and reservoir management challenges in gas reservoirs. Early detection of unexpected water production is critical for ensuring prompt action to prevent accelerated corrosion damage in surface pipelines and facilities if they are not designed to handle the produced brine. Several methods exist for detecting water in pipelines which are based on electrical, electromagnetic, and acoustic measurements. While most of the existing methods are intrusive requiring direct contact between the measurement probe and the flow stream, all such methods suffer from low accuracy of measurements and dependence on water composition and salinity. This paper reviews the various technologies that are in use to detect and measure water production. It also describes the theoretical background and the laboratory testing of a new means for detecting presence of formation water in gas flow lines.1–10 This work is part of a joint collaboration between RasGas Company Limited and Texas A&M University at Qatar (TAMUQ) aimed at developing a device which is: non-intrusive, clamp-on externally on the flow-line, accurate, and independent of saline water composition. This technology is based on neutron elastic-scattering and activation interactions. The laboratory testing is performed using simulated field conditions to determine the feasibility and accuracy of the measurement technique. Based on the laboratory results, a prototype device is planned to be constructed for field testing. Safety aspects of the process application both in the lab and in the field have been thoroughly examined and comprehensive safety measures have been developed and implemented per the health and safety regulatory requirements. The paper also presents the findings from a simulation study using the Monte Carlo N-Particle (MCNP5) neutron flux simulator11 to examine the feasibility of the proposed method and to properly design and optimize the experimental setup and procedure. Introduction Produced fluid in gas fields consists, generally, of gas, condensate, and condensed (zero salinity) water. As production progresses, formation saline water (brine) can be produced with the condensed water. This can affect the operation and safety of the production system by accelerating corrosion and scaling potential, especially in the presence of acidic gases such as CO2 and H2S and the inorganic salts dissolved in the brine. Brine can also lead to emulsion and bacteria related problems. Therefore, it is very important to detect the presence of formation brine in the system as soon as it starts to be produced.

In sour wet gas wells, an iron sulfide scale develops on the carbon steel production tubing wall which significantly retards the rate of metal loss due to internal corrosion. During late field life as reservoir pressure depletion occurs, high flow velocities in the wellbore generate high shear stresses on production tubing walls that can potentially damage the existing corrosion scale and expose the metal to higher corrosion rates. The modeling work done to estimate late field life shear stresses was reported in IPTC-17293-MS and presented in 2014 IPTC in Doha, Qatar. This paper discusses the findings from lab tests conducted in modified autoclaves and a customized flow loop to evaluate the stability of the iron sulfide coating at the predicted late life shear stresses. The iron sulfide scale in the well tubulars was carefully characterized from historical scale composition data as well as analysis of freshly collected samples. This scale was then successfully generated in the lab under carefully controlled conditions. The stability of the generated scale was then tested in High Pressure High Temperature (HPHT) autoclaves and in a customized flow loop by subjecting it to a range of shear stresses. The results provide the first insights into stability of iron sulfide scale under different shear conditions. Findings from this testing program are being utilized to: Develop effective erosion/corrosion management strategy Develop corrosion monitoring and wellbore integrity surveillance programs Define potential future constraints on well production rates Guide materials selection for future wells in the field

Pressure transient tests of wells completed in multi-layer reservoirs have always been and continue to be a challenge for interpretation. Hence, characterizing layer properties from well tests, and determining and monitoring individual layer performance in commingled completions are complex and intensive tasks which could have significant impacts on well and reservoir management. Without accurate assessment of stimulation effectiveness and dynamic skin mechanisms, potential gains in long-term production may never be realized through appropriate action. This paper discusses a hybrid approach for synergizing multi-layer pressure transient analysis with production logging analysis of flow and pressure profiles while accounting for carbonate matrix acidization physics. This approach uses two completely different but complementary tools, which are the existing multi-layer pressure transient analysis option in a pressure transient analysis package and a post-completion inflow performance analysis suite developed by the ExxonMobil Upstream Research Company to analyze carbonate acid stimulation effectiveness for RasGas wells. Based on field experience and acidized wormhole growth physics, RasGas and ExxonMobil jointly developed a new approach to multi-layer characterization using a workflow synergizing pressure transient analysis and inflow performance analysis to analyze post-completion well tests. A field example is described to illustrate the advantages and added value of enhanced understanding of strongly multi-layer producing reservoirs. Background RasGas is one of the major operators of the North Field, offshore Qatar. The North Field is the largest non-associated gas reservoir in the world. The subsurface formation of the North Field, Khuff, is a multi-layered carbonate formation. The Khuff reservoir is formed of four different and non-communicating reservoirs: K1, K2, K3 and K4. As in most carbonate reservoirs, the Khuff lithology is a complex stratification of limestone (much of which is moldic) and dolostone in which the permeability varies by several orders of magnitude. The huge variability of the Khuff reservoir lithology, sometimes even within the same flow unit, is demonstrated by the distinctly variable MDT pressure profiles in a producing (dynamic) reservoir. Defining flow units is often a challenge for geologists and petrophysicists. The work presented in this paper presents a practical approach to quantifying reservoir flow behavior by generalized flow units. Most RasGas wells are commingled producers across all four Khuff reservoirs. These wells are acid stimulated in multiple stages. Stimulations are designed so that some intervals (sub-layers) are treated more than others. This optimized stimulation design is driven by complex reservoir lithology, the large net pay of the reservoir to be treated, and operational requirements for safety and cost effectiveness. The integrated pressure transient/post-completion analysis technique described in this paper was developed based on the company's long experience in dealing with the challenges of monitoring and understanding the well and reservoir performance of commingled producers. Integrated pressure transient/post-completion analysis establishes the baseline performance of a well for proactive assessment of the underlying causes of changes in well performance over the course of production.

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Monitoring individual layer performance (in commingled completions) and integrating the results into an overall understanding of field performance has always been a challenge. Overcoming this challenge allows for a better, layer-by-layer, understanding of the reservoir, and therefore will have a significant impact on well and reservoir management. This paper presents a success case for the integration of a novel approach, and specific applications are highlighted. The Khuff Formation of the North Field is a multi-layered carbonate reservoir formed from four main reservoirs; K1, K2, K3 and K4. As most of the RasGas wells are completed commingled through the main Khuff reservoirs, a hybrid approach for integrating multi-layer pressure transient analysis (PTA) with production logging tools (PLT) analysis of flow and pressure profiles was developed. The process also accounts for the physics of carbonate matrix acidisation. The outcome of this technique has helped RasGas better assess the stimulation effectiveness in commingled wells, and establish baseline performance for individual layers. This work was used to build improved inputs for reservoir simulation models, thus providing more accurate predictions of reservoir performance. Additional benefits of this technique have been: 1) identification of wells with impaired productivity (candidates wells for re-stimulation), 2) a better understanding of the stim jobs (areas for improvement for future jobs), and 3) an improved understanding of log kh vs test kh variation (to understand specific questions on well performance). This paper discusses the outcomes, applications, and the added value of this integrated methodology. The paper will also demonstrate examples where the technology was applied and the value that was added to the ongoing surveillance and future development activities.