Drilling through depleted sands can result in a multitude of problems such as lost returns, differential sticking, difficult logging and/or not being able to reach the target depth. Often curing lost circulation can be difficult and costly as a result of associated nonproductive time and escalating mud costs. Remedies such as cement plugs, squeezes, expandable liner and casing while drilling can be costly solutions. The use of fluid management techniques, team efforts and proper engineering have lead to the development of an innovative approach to prevent problems and avoid the complex processes of curing mud losses and freeing stuck pipe. This new preventative approach with water-based mud has been applied in several fields, while drilling through a series of highly depleted sands and has proven to be very effective in preventing differential sticking and mud losses. Although operationally successful, the geomechanics and the fluid design resulting in these successes are not well understood. A geomechanical analysis indicates that two mechanisms might contribute to the success:The near wellbore region is turned into a non-porous rock because the particles in the new mud tend to block the pore spaces. The theory of poroelasticity indicates that fracturing pressure is increased by reducing the difference between mud pressure and the pore pressure immediately behind the borehole, which for non-porous rock is zero.Because of this blockage, it is possible that the near wellbore rock strength is increased. This strengthening effect decreases tangential stress and increases fracturing pressure. The geomechanics model can be used to define the operational limits of various mud weights with proper drilling fluids design. This model would enable a consistent and focused approach on drilling fluid design to effectively mitigate massive fluid losses associated with drilling through severely depleted sands or in narrow pore pressure/fracture gradient environments. Introduction Lost circulation has plagued drilling operations throughout history. Generally the types of formations that are prone to lost returns are cavernous and vugular, naturally occurring or induced fractures, unconsolidated sands, highly permeable and highly depleted tight sands. Well known lost circulation control techniques such as bridging, gelling and cementing are typically used, with varying degrees of success. These remedies can sometimes complicate the problems associated with lost returns. Attempts to cure lost circulation can be difficult and costly, especially when considering the associated non-productive time. The lost circulation problems related to drilling through depleted sands are compounded by the low fracture gradient in the sands and the high mud weight required to minimize compressivefailure in the adjacent shales. For depleted sands, the best way to manage lost circulation is to prevent rather than cure the problem. This can be achieved using a combination of a geomechanics and a fluids approach. A literature survey indicates that significant work had been done in this area [1–13]. Lost prevention materials (LPM) were developed to increase fracture initiation or fracture propagation pressure. Recently, a theory of using stress cages to increase fracturing resistance has been developed and demonstrated successfully in the field[2]. Sand bridging or "smearing effect" that is generated by casing while drilling techniques has also been applied[4].

Drilling through highly depleted sands can result in a multitude of problems such as lost returns, differential sticking, difficult logging and/or not being able to reach the target depth. Often curing lost circulation can be difficult and costly as a result of associated nonproductive time and escalating mud costs. Remedies such as cement plugs, squeezes, expandable liner and casing while drilling can be costly solutions and are not always successful. The use of fluid management techniques, team efforts and proper engineering have lead to the development of an innovative approach to prevent problems and avoid the complex processes of curing mud losses and freeing stuck pipe. A newly developed deformable sealing agent can be added to a water-based fluid at 2 to 4% volume. It is a modified liquid insoluble polymer that is designed to reduce pore pressure transmission by internally bridging the pore throats of the low permeability sands and shale micro-fractures. These bridging and sealing characteristics will help protect the formation where lost circulation may be encountered. This effective bridging enhances the effective rock strength, hence increasing the formation fracturing resistance. A geomechanical analysis indicates that two mechanisms contribute to the success:The near wellbore region is turned into an altered rock because the particles in the new mud tend to block the pore spaces. Stress analyses using rock mechanics theory indicate that fracturing pressure is increased by increasing the tangential stress around the borehole resulting from the ‘enhanced’ mechanical properties of the altered zone.Because of this blockage, it is envisaged that the near wellbore rock strength is increased. This strengthening effect increases the bulk and tensile strengths of the altered rock and increases the fracturing pressure. This paper will highlight field case histories supported by preliminary laboratory work and geomechanical studies indicate that mud losses associated with severely depleted tight sands can be reduced with the use of the newly developed deformable sealing technology. Some of the field accomplishments of this "internal mud cake" as a bridging/sealing approach are: improved drilling curve, lower well cost, stable and gauge hole, reduction in mud losses and differential sticking and reduction in NPT Introduction Drilling through shallow, highly depleted sands is prone to severe lost returns and differential sticking. Lost circulation and differential sticking problems related to drilling through depleted sands are compounded by the low fracture gradient in the sands and the high mud weight required to minimize compressive failure in adjacent shales. Therefore, drilling deeper to reach new targets in mature fields is becoming more attractive and often presents technical and economical challenges. Designing a well in such complex geological settings often results in additional casing intervals and/or the use of expensive expendable liners or casing while drilling. Typical lost circulation control techniques are costly and may not be applicable. It is better to manage lost circulation by preventing the problem, rather than attempting to cure it. A literature survey indicates that significant work has been conducted on wellbore strengthening[1–13]. Prevention methods have been developed to increase fracture initiation and fracture propagation pressure. Recently, a theory of using stress cages to increase fracturing resistance has been developed and demonstrated successfully in the field[2]. Sand bridging or "smearing effect" that is generated by casing while drilling techniques has also been documented[4].

Hardbanding materials are used to protect tool joint drillpipe against wearin drilling operations. Hardbanding shall resist wear in openhole conditions with a minimum damage to upper casing. Laying down drillpipe for hardbanding repair can significantly increase rig time and tubular costs. All hardbanding products applied for Sincor were wearing out completely after drilling 15,000ft in 50 hours in the reservoir. It was necessary to search for new hardbanding alternatives with an extended lifetime. A field evaluation program was designed to compare wear resistance of different commercial hardbanding materials and toevaluate new techniques for welding tungsten carbide pellets with alloyingwires and for testing of tungsten carbide spheres being laser applied. Hardbanding products were selected upon analysis of wear mechanisms occurring in drillpipe while drilling horizontal wells in Sincor. Wear resistance was monitored in terms of cumulative drilled footage until gauging complete wear ofhardbanding on tooljoints. One of the newly developed hardbanding products wasfinally selected as the best option after considering its superior wear resistance, minimum expected casing damage, and moderate cost. This is thefirst reported successful application of tungsten carbide pellets welded withina hard matrix provided by an alloy wire for hardbanding purposes. Introduction Wear of drillpipe is an important issue for drilling operations in Sincorarea. Wear increases operational cost due to repair of components, rig time tochange out worn down components, and lost of valuable tools. Wear of components has been reported in the tool joint drillpipes since start of operations.Hardbanding and repair cost for a 5,000-ft string can reach up to US$ 150,000 over the string lifetime. With this amount of money and time invested in wear control, high consideration was given to develop material specifications for requesting wear resistant materials. Other solutions implemented in Sincor toreduce drillstring wear are the following:Use of down-hole tools, i.e. Hydroclean drillpipe, for better hole cleaning and a consequently reduction of the backreaming while drilling horizontal sections.Optimization of drilling practices such as mud circulation, use of Hi-Vispills, and backreaming parameters.Use of mud additives, i.e. Ecolane solvent, and heating the mud to reducedrillstring friction.Use of several types of hardbanding materials. This work is aimed to find the most appropriated hardbanding material forprotecting drillpipes in openhole conditions. Minimum casing wear and environmental pollution due to chromium discharge within the drilling fluidswere identified as special concerns. Background Sincor is an operating oil company created in 1997 and it is comprised by Total Venezuela S.A., PDVSA Sincor S.A., and Statoil Sincor A.S. The company started operations in 1998 to exploit the Zuata reservoir located in the Orinoco Belt in Southeastern Venezuela. Reservoir is characterized by an 8-°APIheavy crude oil in unconsolidated sand with extensive shale bedding. Wells are drilled in clusters to minimize environmental impact. Each cluster has an average of 12 extended reach wells having an average horizontal section of 4,450-ft in length. Frequent backreaming is required for hole cleaning purposes. This combination of unconsolidated sand and repeated backreaming as depicted in Figure 1, are the primary causes for wear of drillstring components. Drillpipe is laid down when tooljoint outside diameter is lower than 6–3/8".