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The Hassi Massoud oil field is the largest of its kind in Algeria. The reservoir was discovered in 1956 and produces from a Cambrian-age at approximately 3400 meters depth. It produces 45°API oil from a thick Cambro-Ordovician sandstone formation. This sandstone is extremely hard, abrasive and slow to drill. The reservoir is naturally fractured in some parts. Fractures are either open or plugged with materials such as shale, silica, anhydrite, pyrite and bitumen. Porosity is ranging from 6 to 12%. Generally, the permeability is low with a range of less than 1 to more than 100 md in open-fractures layers Sonatrach introduced Underbalanced Drilling (UBD) primarily in an effort to improve penetration rates. However, all additional benefits obtained from UBD, such as production improvement and reservoir characterization while drilling, will be of an added value. Well OMPZ553 is the 37th well drilled underbalanced in the Hassi Massoud field. In this well, the focus was on production improvement with minimum formation damage while the increased rate of penetration (ROP) was a secondary benefit. Another objective was the evaluation of production while the well is being drilled. This eliminates the need for expensive post drilling production testing, and also to minimize borehole instability specially when drilling in the R2 section of the drain. In order to increase the success rate of drilling and completing this well underbalanced, Sonatrach introduced a new systematic and dynamic procedure. The new procedure consists of:Proper UBD candidate screeningCalculating the actual reservoir pressure before UB mode startsCompleting the well in UB mode This well proved to be the best UB drilled well in Hassi Massoud field in terms of reservoir benefits and characterization. The pre-job UBD candidate screening, feasibility studies and applying the new procedures proved effective in the success of this well. This paper describes in detail the above procedure and presents the successful application of such procedure to optimize production and enhance the ultimate recovery in the Hassi Massoud field. Lessons learnt and challenges encountered will also be discussed in this paper.

The Nezla Field is a faulted anticline that makes conventional drilling challenging due to the presence of fractured and high pressure formations in the Triassic and Ordovician groups, representing trouble zones that jeopardize well objectives, adding costs and operational risks to the drilling process. This adverse condition was observed in the offset wells drilled with problems related to wellbore instability, lost-circulation zones and over-pressured formations leading to kick/loss well control scenarios that endangered the drilling operations and incurred significant Non-Productive Time (NPT). A Drilling Hazard Mitigation (DHM) approach was implemented to offset the risks of both deviating from the well objective and drilling plan. The constraint to drill the planned 12-1/4" section in the well was the unpredictability of the pore/fracture pressure in the transition zone between Tags and Sandy Tags formations, representing a high level operational risk. The most optimum and reliable solution to achieve the goal of drilling this zone without loss of hole size was to set 9¬5/8" casing shallower than planned and then isolate the lower section of Tags formation (abnormally pressurized) with an Open Hole Expandable Liner. Drilling the next hole section through the low pressure formations to set the 7" casing shoe was to be resumed as per the original plan. This allowed the 6" reservoir hole section to be drilled under the Managed Pressure Drilling (MPD) mode. The CBHP (MPD technique) was planned to drill the 6" section through the tectonically fractured Sandstone Hamra Quartzite maintaining the ECD within the drilling window limits initially defined by the predicted formation pressure and the average mud hydrostatic with which fluid losses were experienced in the offset wells. While drilling, these limits were ascertained within the range of 1.26 SG EMW - gas influx and 1.32 SG EMW - fluid losses. The CBHP drilling mode enabled to manage the ECD in between influxes and losses only adjusting the well head pressure to obtain instantaneous changes in the Bottom Hole Pressure while circulation was in progress. During the pumps-off periods, back pressure was applied on the MPD choke by pumping mud across the top of the well to compensate the Annular Friction Loss pressure. Once these limits were reached, drilling progressed with managing simultaneously small gas influxes and tolerable losses; then TD was called since the risk of simultaneous total losses and gas Influxes in the underlying Hamra fault was increasing. This paper describes in detail the DHM technology implemented in this well and presents the successful application of such technique to enhance Nezla field exploitation. Lessons learnt and challenges encountered will be also discussed.

Hassi Messaoud in Algeria has been a major oil-producing field for more than 50 years, with many hundreds of wells successfully drilled. The complex geological structure and varying amounts of depletion mean that 3D geomechanical modeling techniques bring great benefit, particularly in predicting well-bore stability, sanding potential, and hydraulic fracturing. This paper describes such a model for one sector of the reservoir, creating 3D maps of mechanical properties and a 3D stress state that can be updated over time as pore pressures change. Several new methods of applying the results to well design are presented, including the creation of "mud weight cubes" and "sanding potential cubes" to assist with trajectory optimization and mud weight selection, and to provide limits on safe drawdown.

The Field was discovered in 1960 during the exploration phase, this field is located between the Hassi Messaoud field and Rhourd de Nouss Central Field in the Triassic Basin in Algeria. The field represents many challenges for conventional drilling due to the complexity of the geological structures, one of these is the Hamra Quartzites formation; a gas reservoir sandstone highly tectonically fractured. The drilling history of this formation shows events of total fluid losses leading to gas kicks due to the loss of hydrostatic head in the annulus. A 6″ hole section in NZ-XX well was planned to be drilled under the Constant Bottom Hole Pressure (CBHP) technique, throughout the Gres de Ouargla and the Hamra Quartzites formations; bounding the drilling window by the estimated formation pressure as lower limit, and the fluid losses pressure (hydrostatic pressure of mud used in offset wells) for the upper limit, both estimations were done at the top of the reservoir. The drilling window for Managed Pressure Drilling-MPD was validated by determining the Bottom Hole Pressure where both, an influx from the formation and fluid losses occurred. These values were later used to establish the target Equivalent Circulating Density-ECD to drill the hole accordingly. The ECD management was achieved by controlling both, the surface back pressure and the annular out-flow; monitored in real time. The Bottom Hole Circulating Pressure-BHCP changes recorded in a Pressure While Drilling-PWD tool, placed in the Bottom Hole Assembly-BHA. As the drilling progressed, fluid losses were experienced and instantaneously controlled by reducing the ECD. Despite the lower and upper MPD window limits converged, drilling continued managing losses as no open operating range existed. As a contingency for this scenario, switching to the Flow Drilling technique (UBD) was proposed and planned, but due to environmental restrictions, flowing the well while drilling was not possible. The MPD operations in NZ-XX successfully achieved 191 meters of open hole; then TD was called due to a combination of increasing losses – gas influx conditions and increasing risk of total losses in the underlying Hamra faulted structure. This paper describes in detail the successful MPD application which is considered a start he drilling technology to enhance Nezla field exploitation. Lessons learned and challenges encountered will also be discussed in this paper.