With the majority of today's "new" hydrocarbons increasingly found in technically challenging, complex and in many cases lower quality reservoirs, it's long since been agreed there is no more "Easy oil". It's that fact, coupled to the industry wide challenges associated with conventionally drilled wells in mature and depleted reservoirs which have led in recent years to the very significant advances seen in the Advanced Drilling Techniques (ADT) and Technology arena. ADT provides a suite of tools and techniques which have enabled the technical and commercial development of numerous oil and gas reservoirs worldwide which would have not otherwise been exploited. ADT comprises of the following techniques: Managed Pressure DrillingUnderbalanced DrillingCoiled Tubing DrillingThrough Tubing Rotary Drilling (Conventional and HPHT)Subsea Through Tubing Rotary Drilling According to one recent industry report some 67% of the world's daily oil production comes from mature fields, therefore in order to not only sustain but improve upon current production levels, field life extension is not optional but an absolute necessity. Historically however, most Operators due to cost and complexity of well delivery have not fully exploited their mature assets consequently failing to reach their full potential. Therefore, in order to not only sustain but increase current production levels to meet the increasing demands, operating companies must pay greater attention to their mature fields and their resources development options. The above coupled to the fact that in almost every conventional drilling operation there is risk, a potential to; damage well productivity (formation damage), encounter lost circulation; suffer differential sticking and many other related conventional drilling problems any of which can be exaggerated in a mature drilling environment as a function of depletion. Its here, when applied with an expert system for candidate reservoir screening, technique selection and improved reservoir evaluation technologies, ADT provides realizable and available EOR and IOR options in accessing ‘conventionally’ or commercially stranded reserves. Further, when fully coordinated with the neseccary subsurface disciplines an ADT solution will add measurable value by; improving production, enhancing ultimate recoverable reserves, even possibly reduce overall development cost all improving net present values. Popular perception is we need new technology to sustain and drive the industry forward in meeting the global demands placed upon it; in truth if we look; much of the required technology is available now. The thing we, the industry, need most is the opportunity and most importantly the courage to deploy it. This paper will challenge us in our perceptions and highlight how we can mitigate the risk applying smarter drilling options such as those offered by Advanced Drilling Techniques in the hydrocarbon bearing formations.

Drilling depleted reservoirs can present many challenges from a drilling, completion and production perspective. Formation damage due to increased overbalance for example, is well documented as a particular concern. But could we see some drilling benefit from increased formation damage at higher overbalance? This paper will outline experience in drilling depleted reservoirs and discuss the impact of formation damage on well productivity, injectivity and drilling performance. In several examples, the benefits of formation damage outweigh the deficits and we propose a planned approach for future wells in depleted reservoirs. Formation damage is measured in the same way as for assessment of the productivity or injectivity impact but the data is applied to a different challenge. The additional pressure drop in the near wellbore area as a result of formation damage can protect the reservoir and minimise fracture propagation. Whilst formation damage can be important in depleted reservoirs it is largely irrelevant if wells cannot be drilled. With the method proposed wells can be planned, drilled, completed and produced (or injected).The paper proposes better understanding of the impact of formation damage in order to enable drilling, completion and development of depleted reservoirs or intervals and proposes a new methodology to use formation damage as part of a well planning workflow. IntroductionIn terms of delivering a functional, commercial wellbore the drilling process and the fluid systems employed therein has the single biggest effect on well quality and in turn well productivity. As a function of that we strive where possible to mitigate the influence of drilling induced well bore formation damage. However, there is a paradox here in that there is a case for planning and deliberately inducing formation damage as part of a well planning workflow, consequently strengthening the depleted section of the openhole as a function of improved hoop stress strengthening the wellbore to facilitate otherwise un-drillable wells.The objective of this deliberate act is to strengthen depleted reservoir or naturally weak formations (e.g., chalk) that must be drilled through to access reservoir(s) of interest as part of the 'transport length' in typically infill drilled wells to allow wellbore to access deeper and higher pressure horizons. In cases like this, the mud weight required to maintain borehole stability across exposed shale sections or to drill through objective sand will create excessive ECD across depleted sand higher up in the open hole. Here, wellbore strengthening will help increase fracture pressure in the depleted sand and sustain higher mud weight.Mud formulation for wellbore strengthening in the reservoir to be produced will necessarily differ from what can be used drilling through depleted sand or fractured Carbonates in the transport length section of a well. In these non-reservoir intervals, it is often "desirable" to drill with mud systems that promote formation damage. Some mud systems, such as SILICATES, a...