Water production control is a key issue in most mature reservoirs worldwide. Many techniques have been developed to achieve this purpose. Water Shut-off (WSO) treatments using crosslinked gels have proven to be an effective alternative. When appropriately designed and applied, these systems generate flow restrictions in high permeable or fractured formations that bypass water from highly saturated zones (injection water or natural brines). WSO treatments efficiency depends on several aspects as reservoir fluids flow patterns, rock petrophysics, formation heterogeneity, and WSO gel characteristics. This last aspect is adjusted to optimize the treatment based on experimental tests performed in the laboratory. This paper presents an experimental methodology to evaluate and adjust WSO polymer systems according to operational and treatment performance requirements. These studies go from qualitative gel consistency and fluid compatibility bottle tests, to rheological characterizations to determine viscosity variations and gelation time (outside porous media tests), as well as flow tests performed on formation and Berea core plugs at reservoir conditions (inside porous media tests). These properties are highly important to avoid early gelations and, at the same time, assure the appropriate WSO placement in the reservoir. Viscoelastic properties such as G* (complex modulus), G′ (storage modulus) and G″ (loss modulus) define the gel strength and provide structural information such as crosslinking density. These parameters are essential to design the gel formulations (polymer and crosslinker type and concentration) depending on the operational and reservoir requirements. Finally, the flow tests performed on core plugs show the changes in water and oil permeability after injecting the treatment. This information is used to calculate the residual resistance factors to water (RRFw), oil (RRFo) and the gel resistance index (GRI). These parameters define the treatment blockage degree and allow estimate probable well production response as well as the best production regimes to extend the treatment life time. This methodology was applied on a new WSO gel system, developed for a wide range of applications. The effect of polymer concentration, temperature, salinity and flow rate are examined in detail. Experimental tests are many times underestimated when planning a WSO job; however these tests will always provide valuable information that will increase the chances of successful water shut-off treatments. The connection between laboratory and field parameters and its influence in the oil and water productivity were analyzed.

Class A cement has been used for cementing surface casings and shallowwells. API Specification 10A classifies the well cements into three categories, ordinary, moderate and high sulfate resistant, depending primarily on theamount of tricalcium aluminate (C3A) present in the clinker. Cementclass A (ordinary) presents no C 3A restrictions. On the other hand, moderate and high sulfate resistant cements should contain less than 8 and 3 %C3A respectively. Under certain conditions, sulfate ions will chemically combine withtricalcium aluminate giving rise to an expansive reaction that can cause cementdistress. This process depends on cement permeability and environmenttemperature. Several research studies conducted in this field have proven thatthe degradation process decreases as temperature increases and can becontrolled lowering the cement permeability. The purpose of this study is to analyze the sulfate attack mechanism atseveral bottom hole conditions in order to ensure an appropriate well isolationdurability performance using cement class A. Specimens prepared with APIcements class A and G were exposed to solutions containing sulfatesconcentrations ranging from 0 to 30000 ppm and temperatures of 89.6 and 183.2°F (32 and 84 °C). The specimen's length and weight variation was evaluated periodically. The presence of expansive phases (ettringite) was detected bymeans of SEM and EDAX analysis. A model to predict the cement degradation process due to sulfates attack is proposed. The cement specimens (A and G) showed no significant expansion during thefirst 240 days of exposure, however growth of secondary ettringite in cementpores was detected by SEM analysis. The sulfate degradation process requires acertain incubation period before the cement pores get completely filled withettringite. The use of pore blocking additives increases the sulfate resistanceof cement class A, ensuring appropriate performance and durability. Introduction Sulfate attack is one of the degradation mechanisms of cementitiusmaterials(1). This phenomena has been and continues to be the subject of many investigations, as it may cause the premature failure of civiland highway concrete infrastructure(2–4). As a consequence, thefirst publications and standards addressing this topic have been orientated tothe building construction industry(5,6). Based on these findings, API Specification 10A(7) proposes a classification for oil wellcements that is similar to that established by ASTM and other European codes. According to API, oil well cements are divided into three groups, ordinary, moderate and high sulfate resistance, depending primarily on their chemicalcomposition. Table 1 presents the chemical requirements for cement class A andG as specified in API SP 10A. The Process of Sulfate Attack The hydrated calcium trisulfoaluminate(C3S.C3A.H32), commonly known as ettringite, is a crystalline meta-stable hydration product of Portland cement. During thefirst 24 hours of hydration, the tricalcium aluminate(3CaO.Al2O3, also referred as C3A in thecement nomenclature) reacts with gypsum (CaS04.2H2O), added to the clinker to regulate the C3A rate of hydration, to formwhat is known as primary ettringite (Eq. 1).Equation 1 As cement hydration takes place the amount of gypsum decreases and part ofthe ettringite is transformed into calcium monosulfo-aluminate hydrate asindicated in equation 2.Equation 2 This reaction also depends on several factors as the ratio between S04=/C3 A, the pore solution alkalinity, thewater to cement ratio (w/c) and the environmenttemperature(1,3,8–10). When hydrated cement is placed in anenvironment containing high sulfate concentrations, as could be the case ofmany formations, the calcium monosulfo-aluminate hydrate and the calciumhydroxide present in the cement paste will react with the sulfate ions comingfrom the environment to form what is known as secondary or delayedettringite (Eq. 3).

The use of Glass Reinforced Epoxy (GRE) casing has increased significantly during the last decade, primarily on secondary recovery water injector wells. Corrosion resistance is this material main advantage when compared to steel. Almost one hundred wells have been completed in the Neuquén basin, Argentina, during the past five years.This paper presents the experience obtained after cementing and completion of 70 GRE cased wells. Improvements on cement slurry mix designs, mud cleaning preflushes systems and best practices to ensure successful stimulation conditions (acids and fractures) are provided.The work is supported by a laboratory study focused on the GRE casing to cement bonding performance evaluation and a finite element numerical simulation analysis of the down-hole service conditions achieved during stimulation jobs. This study considered the influence of GRE, cement and rock mechanical properties, the mud-cake removal conditions, as well as different bonding conditions. A comparison between GRE and steel cased wells is presented.Cementing results were improved by casing centralization, increasing the preflushes aggressiveness and using low density slurries. Bonding experimental results showed that original GRE external coating attempts against cement bonding strength.The numerical simulations show that when GRE casings are subjected to high internal pressures, its elastic behavior (Young modulus ten times lower than steel) generates overloading on the cement annulus. This condition could generate cracks that will propagate along the annulus creating communications paths between close perforated zones during stimulations treatments. This situation is even worst when poor formation mud-cake removal takes place.

TX 75083-3836 U.S.A., fax 01-972-952-9435. AbstractDuring the well service life the cement isolation is exposed to extreme conditions that can cause its premature failure. Certain well completion operation as perforating and hydraulic fracturing, the changes in temperature and pressure during secondary recovery or the mechanical stress originated by formation displacements may cause severe damage to the cement isolation. The mechanical properties (compressive and tensile strength, toughness, Young modulus and Poisson ratio) of different cements were evaluated in order to establish their best service performance. Typical slurry designs were tested focusing the attention on the effect of certain additives such as latex, fibers and other polymers used as fluid loss control or dispersants. The cement mechanical properties were determined according to ASTM and API standard test methods. The cement toughness was evaluated following the API RP 43 standard for testing well perforators. The experimental results show that the mechanical properties of cement are strongly dependant on the particular additives used when preparing the slurry. Even when cement with no admixtures presents high compressive strength it also shows a fragile behavior with limited strain and low toughness. The use of latex improves the cement elastic behavior although it does not better its impact resistance. On the other hand, the addition of polymer fibers improves the cement toughness and its elastic behavior. As it was demonstrated by well testing profiles run before and after perforating, the addition of fibers improves the cement performance when exposed to the different events that may damage the isolation during the well service life.

This paper describes the magnetic effects studied at CEM in their realization of a primary standard for dynamic force calibration using sinusoidal excitations of force transducers, although they can also affect any sensor with an electrical output mounted on an electrodynamic shaker. In this study the electromagnetic behaviour for the interaction between sensor and shaker or a similar source of magnetic fields is explained and a solution to minimise this interaction is also included.