There has recently been a resurgence in the use of water based muds containing sodium silicate for drilling reactive shale sections, particularly in the North Sea. The performance of these silicate water-based muds (SWBM) has been mixed: they are extremely effective in inhibiting swelling and dispersion of claystone and chalk, however some concerns exist over the stability of the system in terms of fluid properties, long term wellbore stabilisation and lubricity. This paper details new results, previously unreported, which give a better insight into the mechanism of clay stabilisation using SWBM. Recent literature has suggested that silicate fluids are as effective as oil-based muds (OBM) in wellbore stabilisation. This paper describes research and development indicating that silicate precipitation occurs within shales to form a barrier or membrane that hinders ion movement. However, there are distinct differences between the efficiency of membranes produced by oil based and silicate water based muds. Results are included which demonstrate that the ion- exclusion membrane is not as effective with Silicate systems as it is in OBM. New core flow experiments demonstrate that a permeability reduction with silicates and a slow rate of ionic equilibration are the principal causes for the osmotic barrier seen in swelling tests. Further results indicate a change in the physicochemical nature of clays after exposure to high pH silicate fluids. It appears that redistribution of alumino-silicate occurs which may play an important role in the inhibitive nature of these fluids. These evaluations are placed in context with well data in which primary considerations are the nature of any lost time incidents and overall SWBM performance. P. 897

Over the years the industry has seen major changes in drilling fluids technology, especially in the field of organic-phase fluids (OPF) such as diesel, mineral oil and synthetic hydrocarbon base fluids. Environmental concerns have driven the development of ‘traditional’ oil-based fluids away from diesel and through to the less toxic, more biodegradable synthetics such as esters and olefins. Many companies are now considering the overall picture regarding the disposal of wastes and are looking for alternative uses for drilling by products, thus turning wastes into useful raw commodities. While organic-phase fluids evolved, research into water-based fluids (WBF), which are generally considered less harmful to the environment, concentrated on duplicating the technical performance of oil-based fluids, the absence of oily discharges being the environmental benefit. A more holistic view of the overall impact of WBF discharges and concerns about the persistence of some WBF chemicals has now focused development on alternative ways to further reduce the impact of water-based fluids on the environment and accelerate recovery of the impacted areas. The key to reducing the environmental impact of drilling fluids is typified by the standard waste management hierarchy. The areas to consider are source reduction, recycling/re-use of the product, recovery of useful or valuable materials and treatment prior to disposal. The focus of this paper is how new technologies can be used to bring about these changes and to discuss the various ways in which the amount of drilling fluid by-products can be reduced. The paper also describes ways in which new drilling fluid developments such as salt-free drilling fluids or the use of colloidal weighting agents can be designed to optimize waste management and reduce the amount of waste. These technologies also facilitate the re-use and recycling of drilling fluids and their components. Introduction To significantly reduce the environmental impact of drilling operations, the process of drilling a well needs to be viewed holistically and environmental benefits need to be tied to financial savings. For example, which is more advantageous, drilling quickly with an "expensive" fluid that saves four days rig costs and thus reduces overall CO2 emissions or using a "low-cost" fluid which does not perform as well as the expensive one and results in increased rig costs and emissions. It is equally important to ensure that the fluid used to drill the reservoir section maximizes recovery of the available hydrocarbons and reduces the need to drill more wells. This paper uses some of the concepts of life cycle analysis1 to consider the total impact of the various stages of drilling. Factors that should be considered when trying to optimize the overall waste management strategy include total materials used as well as solid, liquid and gas emissions. One of the key points of an effective waste management strategy is the waste management hierarchy. Figure 1 ranks the desirability of each stage of the hierarchy. The best solution is to avoid producing the waste, but if this is unavoidable, then the amount of waste produced should be minimized. Steps should then be taken to maximize the recovery, re-use and recycling of materials before reducing the amount of material for final disposal2. Avoid - Reduce Well Intervention Reduction of the total number of operations/interventions required to extract hydrocarbons will result in a reduction of both the total energy budget and the overall environmental impact. It is also important to recover the maximum amount of hydrocarbons (or energy) from the reservoir. This means that in addition to drilling to the reservoir quickly and efficiently, it is also necessary that drilling practices do not reduce the productivity of the reservoir causing an increase in the overall energy costs.

Thispaperwasppnred forpraaentatlon at tha 1995SPE/lAOCDrllllng QmferencaheldIn Amererdam, 2E Febrwry-2 March1SS5. ThBww wa8 D9med b fm-atbn by an sp~m PKIOMM~mm~~~im *~in~c ontelned In an abstract eubmHted bytheauthor(s). contents ofthepew, egpresented, hew notbeanrwkwed bytheIntematicaal Aswcietbno~~_lliw.$gtfactom orthnSocktYOfp-m EIWIOWSe~we @@ to~~~W t~a@h@s), Tm eteriel, as presented, *~~ly fefl@ anypOSlflOII IX ffI13 SPE of mm, fiik Offk#S .. -_L_ .---++ ., QDCIIAIY RUAt.a am IMIbbd to mbbatkn rd6w' by EdHc+lel Commltt.ws oftheSPEacd IADC.P%MIis4011 tocopyis reetfktedto an * % fi-W"\~-&w=.%=~;%;Y"%-~"&~~-k-=;= shdd contain conspkuoua acknowledgment ofwhereandbywhomthepaperispmwntcd.Writel.ibrefkm. SPE,P.O.SOX .922SS8, FIM*, TX 7~0 u.S.A.Tefex,15S245SPEUT. ABSTRACTThere are many aspects of water based muds (WBM) which must be improved before they can truly approach the performance of an oil based mud (OBM). OBMS provide increased chWing performance by combining shale hydration inhibition, drill string lubrication, reduced stuck pipe risk, low formation damage, corrosion avoidance and high temperature stability.The importance of these attributes is briefly discussed.Although OBM perfonmmce may not yet be replicated, an integrated approach does allow the target to be approached.

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