Prediction of new perforation intervals in a depleted reservoir to achieve the maximum productivity: A case study of PNN logging in a cased-well of an Iranian oil reservoir

Pulsed neutron-neutron(PNN)logging is based on emitting neutrons into the near-wellbore zone and computing the neutron count decay due to scattering and capturing.The main application of this logging tool is to determine the current oil saturation and to detect channeling in perforated and non-perforated intervals behind the casing.Correct interpretation of the results obtained from PNN logging enables engineers to predict new perforation intervals in depleted reservoirs.This study examines the application of PNN logging in a well located in one of Iranian oil reservoirs.The interpretation procedure is described step by step.The principle of the PNN logging and the specifications of the tool are discussed and the applications of PNN logging in evaluation of oil saturation,identification of water flooded zones and prediction of potential perforating zones are described.Channeling is also investigated between all layers,good and poor oil zones are characterized based on the calculated oil saturations and new perforation intervals are suggested with the aim to boost oil production from the reservoir.The results of this study show that zones 1 to 5 having low oil saturations,are interpreted as depleted oil zones.Zones 6 to 8 are interpreted as good oil zones having high potential to produce oil.Zone 9 is interpreted as a water zone.

Geological characteristics and key exploration technologies of continental shale oil sweet spots: A case study of Member 2 of Kongdian Formation in the Cangdong sag in the Huanghua depression, Bohai Bay Basin

Under the general trend of stepping-up oil and gas exploration and development in China,the unconventional oil and gas resources such as shale oil and gas have become an important alternative.Abundant continental shale oil resources are developed in Member 2 of Kongdian Formation(Ek2)of the Cangdong sag in the Huanghua depression of the Bohai Bay Basin which has complex structure,strong heterogeneity,and large buried depth,thus,the geological characteristic of shale oil accumulation and key exploration technologies are investigated on base of the system coring of 635.8 m,centimeter-level fine description and analysis of over ten thousand samples,therefore,the“four accurate”technologies have been developed,including the accurate selection of sweet spot areas,accurate drilling of sweet spot layers,accurate fracturing of sweet spot layers and accurate measure of fracture-rich sections.The results show that the continental shale strata in Member 2 of Kongdian Formation can be divided into three types:felsic shale,limy dolomitic shale and mixed shale.The Member 2 of Kongdian Formation is characterized by diverse mineral components,abundant laminae,good source rocks and medium thermal evolution degree,tight reservoir with rich micropore and microfractures,high oil saturation and brittle mineral content,indicating good prospect of shale oil exploration.Through sedimentological study,TOC and Ro evaluation,brittle mineral calculation,and seismic fusion inversion,a total of 126 km^(2) of Class I sweet spots in Member 2 of Kongdian Formation was delineated comprehensively,which guides horizontal well deployment(Well GD1701H and Well GD1702H).The drilling rate of sweet spot of these two horizontal wells is up to 96%by tracing thin layer through fine calibration,locating compartment through fine inversion,ensuring window entry through precise positioning,and tracking sweet spot through adjustment.The “one-excellent and five-highs”criterion is used to select perforation points to realize differential designs of fracturing intervals and clusters.Micro-seismic and potentiometry monitoring show that the artificial fractures formed by volumetric fracturing are 300e400 m long and 120 m high,and control a volume of about 0.07 km^(3).The maximum daily oil production of two horizontal wells is 48 t and 66 t respectively to realize the economic exploitation of shale oil reserves controlled by fractures.The shale oil exploration in Member 2 of Kongdian Formation shows that the continental shale oil has great potential of exploration and development,and the above technologies are critical and effective for shale oil efficient recovery.