Experience of Drilling the Horizontal Well VLD-1152 in Lagunillas Formation, Block IV, Lake Maracaibo Basin, Venezuela.
The main objective of the horizontal well VLD-1152, located in Block IV, was to improve recoverable reserves which was impaired by pressure depletion and reservoir heterogeneities. The well represents an important challenge because it is the first horizontal well drilled in a depleted pressure area and it was drilled within a small productive interval of 25 feet thick only.
A pilot area was selected after a detailed multi-disciplinary study by geologists. petrophysicists and reservoir engineers. New 3D seismic interpretation revealed a structural model that conformed well with pressure behavior of the area. New information from well VLD-1112 were utilized to update the petrophysical properties and the volumetrics These data were input to develop improved reservoir description and build a reservoir model for flow simulation.
The results indicated that Layer VII is the most important drainage target. The principal reasons for selecting this unit were, good mechanical stability of the rock, absence of a water front and a secondary gas cap and the presence of a regional shale ar the top that might be used to navigate drilling.
Despite some operational problems encountered in drilling, the results were mostly satisfactory. The entire pay was penetrated and the geology and petrophysics of the drilled area came in line with our model predictions.
A pilot area, containing approximately 30 wells located in Block IV in Lake Maracaibo Basin,was selected as the site for a horizontal well (Fig.1). The target reservoir, VLC-52/VLD-192 Lower Lagunillas, commenced production in 1957 with well VLD-192.
The reservoir, which is stratigraphically divided into L, M and N sands, has not been uniformly drained. Since 1960, most of the wells have been completed in the L and N sands; therefore, the M sand has been less depleted. (Fig. 2) Production declination was very intense and was partially controlled by a gas injection program in 1967. Dropping pressure however continued until getting 1000 psi (Fig. 3)
The drilling of VLD-1112 well at south of the selected area, contributed with valuable information to validate the petrophysical parameters and calculate a new OOIP number which was found to be 20 % greater than the initial estimate of 264 MMSTB.
Once the new geological model and petrophysical parameters were defined, the more prospective area with less operational risk was selected. The output was used as information to develop a dynamic model for the simulator. The results provided well defined boundaries conditions and indicated the absence of an independent aquifer.
The selection of the zone was based on a combined evaluation of different criteria of orientations, lengths and restrictions for the horizontal well. This zone showed low values of porosity and permeability and a depleted reservoir character, justifying drilling of horizontal wells in order to improve oil recovery and maximize the production rate. The recommended location was GOF-3.
The main target is Unit VII of M Sand Lower Lagunillas Member. This sand has an potential of 1200 STBOD, and is expected to have a water cut of 5% and a GOR of less than 1000 SCF/STB.