The Serang Field, offshore East Kalimantan, Indonesia was discovered in 1973. Production started in 1993. Although it is a mature field with 120 wells, drilling still faces challenges in the form of severe lost circulation and stuck pipe events. Side tracks often need to be drilled and drilling budget overruns can be significant. The 2006 drilling campaign of 5 wells saw the loss of several BHAs and needed 4 sidetracks, due to stuck pipe events. In order to improve the drilling operation and to uncover root causes of the losses and pack-offs, a detailed geomechanical evaluation was conducted. The study began with a comprehensive data audit and drilling event review. All the captured information and log data was then used to create a Mechanical Earth Model (MEM) for wellbore stability planning of future wells. Key findings of the study were that lost circulation occurred in high permeability zones in shallow carbonates (8-1/2" intermediate hole section) and were not caused by drilling induced fractures. A contingency plan was developed to drill to section TD with sea water, should losses occur. Breakouts, aggravated by low mud weights, lost circulation events, high deviation and slim hole contributed to poor hole cleaning, which caused the packoff incidents in the 6 1/8" sections. Safe and stable mud weight windows were established to mitigate hole collapse and stuck pipe. Since losses can occur even at low mud weights but do not usually have severe consequences, the team decided it was more important to focus on avoiding breakouts and improve hole cleaning with higher mud weights, improved drilling fluids with stress cage system to drill through depleted reservoirs, controlled drilling, ECD management to prevent formation breakdown and the use of Rotary Steerables to improve hole cleaning. The recommendations of the study were incorporated during a 3 well drilling campaign in 2009. All 3 wells were drilled and completed within budget and without stuck pipe incidents.

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A novel methodology has been developed to evaluate low resistivity pay reservoirs in very thin, laminated sand-shale sequences. This technique combines information from both high and low resolution logs to model the petrophysical properties of thin bedded formations. The result is a set of modeled high resolution logs that can be used to yield more accurate estimations of porosity, water saturation and permeability. A high resolution and a low resolution log response are selected and binned into discrete lithofacies. The average low resolution log responses are statistically calculated for each lithofacies. An initial model is generated by using the high resolution lithology index to select the corresponding low resolution response for each lithofacies, resulting in a set of high resolution logs for each input log. By applying a corresponding vertical response filter to the high resolution log, a synthetic log is created which can be compared to the original. A minimization technique is used to adjust the high resolution responses such that the synthetic and actual logs agree. Since there are an unlimited number of high resolution logs which could result in the same synthetic response, the process is constrained using limits defined for each lithofacies. Evaluation of hydrocarbons in place is then performed on the resulting model. This paper documents examples in deep-water turbidite reservoirs where thin beds on the scale of a few centimeters were evaluated using this technique. The observations were consistent with core data where this was available. Thin bedded silt and shale laminae had a disproportionate effect on standard resolution measurements due to the abundance of montmorillonite clay which caused elevated neutron and suppressed resistivity responses. The constrained thin-bed analysis yielded considerable enhancement of hydrocarbons in place compared with the evaluation using only standard resolution measurements. Thin bedded laminated reservoirs occur in many hydrocarbon provinces. The technique described in this paper provides an alternative method for evaluating these formations, helping to reduce reserves uncertainty during a time where accurate reserves evaluation continues to receive high attention. Introduction Formation evaluation in thin shale-sand sequences has been a challenge. Thinly laminated pay zones are frequently overlooked when using conventional formation evaluation. Identification of deep-water turbidite sequences and their productivity are affected by clay characteristics, mineralogy, the unconsolidated nature of the sediments and low resistivity contrast pays. Extensive efforts, involving both monetary and human resources have been made in the past decade for identification and enhanced evaluation of such thin shaly-sand sequences. Motivated by the initial success of identifying and evaluating the pay zones encountered in the deep water exploration block of the Krishna-Godavari Basin, east coast of India, shown in Figure 1, the major challenges were to extend the exploration campaign to the adjacent deep sea areas and to estimate the reserves associated with the thin bedded shaly sands. Evaluation of thin beds that are less than the resolution of standard logs was the greatest challenge. Pay zones were identified by the integration of high-resolution logs and image data with seismic. Inverse modeling the thin sand-silt-shale formations using total clay content from X-ray diffraction (XRD) analysis of cores, it was possible to estimate a realistic hydrocarbon saturation within the pay zones. A novel technique of enhancing the resolution of logs to the level of microresistivity imaging tools helped us in the estimation of log response in such thinly laminated pay zones. The following sections describe the geological setting of our case study, the methodology of our new technique, the results and summary and conclusions.

Drilling horizontal wells in soft formations can pose significant risks that require careful planning and execution. During 2014, Virginia Indonesia Co. Limited (Vico) successfully completed two surface-to-inseam horizontal wells to appraise coalbed methane (CBM) production potential on their Sanga Sanga license in East Kalimantan, Indonesia. Both wells passed through soft shales and coals that exhibited breakouts in offset wells, in addition to heavily depleted zones exhibiting large fluid losses in an area well known for shallow gas blowouts. Geomechanical analysis of information from nearby offset wells was used to determine the mud-weight window and fluid properties required to effectively manage these conditions. The results were incorporated into the preliminary well design and planning, and with model matching carried out in real time while drilling operations were underway, any deviations in wellbore integrity were managed as they arose. The drilling success was, in large part, a result of extensive preplanning and a regimented approach to how the wells would be drilled and any instability dealt with promptly. In addition, real-time monitoring that identified deviations from model-based predictions provided invaluable information for planning subsequent wells. The methodical approach to planning and execution of these wells led to their successful completion, with the results potentially reshaping the Indonesian CBM and energy industry.

Madanam field in Cauvery basin in the east coast of India, has fractured gneissic basement. As exploration focus moved to unconventional reservoirs, the gneissic basement of Madanam was seen as a potential reservoir. However, ambiguity existed about the fluid flow through the basement. For example, in Madanam field, one well (well A) flowed whereas another well (well B) located 8.5 km away had minor flow from the basement reservoir that lasted 2 days. The main purpose of this study was to find possible reasons for this anomalous behavior. This study was conducted by integrating sonic and image measurements with a geomechanics workflow to identify critically stressed open fractures. Further, this work aims to provide a fit-for-purpose solution to optimize and prioritize testing zone selection in near real time.