A Case History – A New Stimulation Technique Enables Sustained Production Enhancement in Mature Lenticular Reservoir

Abstract

Romania is a key pioneer in oil and gas industry with a history of more than 150 years'experience. Many of the oil fields discovered in the early days are still being produced. Extending the production life of mature fields presents a variety of challenges including low reservoir pressure, high water cut, limited well data, aging completions and bypassed pay. The target field is a mature oil field situated in the heart of Romania that has been operated since the 1960s and exhibits many of the aforementioned issues. This paper describes the reservoir, exploitation difficulties and new techniques applied to overcome the key challenges to effectively producing this aging asset. Production enhancement in mature assets require new approaches that can address key challenges and risks associated with the reservoir and completion age. Application of conventional can easily lead to failures including ineffective stimulation, completion failure, screen-out, and increased water cut, all causing difficulties to put wells back in production and resulting in disappointing results. In mature fields, a different approach is required. This paper details first time application of the flow channel hydraulic stimulation in one of the wells in the field, describing the importance of well candidate selection phase, engineered design, execution, and evaluation. The applied channel hydraulic stimulation combines geomechanical modeling with intermittent proppant pumping and degradable fibers to obtain heterogeneous placement of proppant within the fracture. A post job production evaluation compares the production after the conventional treatments versus post flow channel hydraulic stimulation job. The results for all conventional hydraulic stimulation treatments show a steep production decline rate, while the positive impact of channel hydraulic stimulation is apparent resulting in higher initial production and an overall slower production decline. The productive reservoirs besides of low reservoir pressure, are characterized by an increased degree of lamination. The target interval is usually described by a sequence of marls and lenticular streaks of sandstone and shaly-marly sandstone. Conventional hydraulic stimulation treatments have had a marginal effect in this reservoir. Due to the variable lithology, gained limited connection through conventional ways of stimulation and/or perforation end up in quick depletion and production decrease. Channel hydraulic stimulation was applied for the first time in this field and may now be considered to be an efficient way of enhancing production in this and similar reservoirs.