The production performance of the horizontal well VLC-1184 has proved to be a successful strategy for increasing oil productivity in the Lower B Sands of of the Eocene, VLC-100 Reservoir, located in Block III, Lake Maracaibo. The reservoir is located in a small structural trap bounded by an active aquifer. The Lower B Sands in the VLC-100 area is a mature oil reservoir, where recently drilled vertical wells were found to produce significant water cut within one year of completion. Therefore, the horizontal well VLC-1184 was drilled in the updip area of the reservoir to avoid premature water breakthrough into the well by water coning. To acquire additional reservoir information, a pilot vertical well was drilled prior to the drilling of the horizontal well. The information included 360 feet of core, a complete suit of modern logs and pressure information. The analysis and integration of these data provided a detailed reservoir characterization and wellbore stability analysis for the successful drilling and completion of this horizontal well. Information from the cuttings and LWD during drilling was used to make any adjustment to the original planning.
The horizontal section is 1237 feet long and was completed open hole. The mechanical completion included the installation of two sensors for measuring the bottomhole pressure and temperature in real time for monitoring the well performance. The well has cumulated 763 MSTB, in 13 months, and at the present is produces 1400 STBOD with 15% of water. This result has encouraged the analysis of additional opportunities for horizontal drilling in the same reservoir.
Drilling a horizontal well provides a good opportunity for increasing productivity in mature oil fields. The Lower B Sands of VLC 100 reservoir, Block III of Maracaibo Lake, Venezuela (Fig. 1) is one such reservoir. It has been producing for more than 30 years, and newly drilled vertical wells in this reservoir were producing at high WOR only after 1-2 years of completion. Therefore, the prospect of drilling additional vertical wells for draining the remaining oil becomes uneconomic. A multidisciplinary team recommended drilling a horizontal well to prevent premature water arrival at the well and thereby drain this area more efficiently.
This well was located up-dip in the structure, parallel to the normal fault that bounded the reservoir to the north (Fig. 2). The biggest limitation for carrying out this plan was the necessity of additional reservoir information. Geological uncertainties along the horizontal section were the critical information lacking in this case. The 3-D seismic survey of the area did not have the appropriate stratigraphic resolution for lowering the uncertainty risk nor a sedimentary conceptual model predicting the range of uncertainties could be constructed because of lack of core information.
For obtaining additional reservoir information, a pilot vertical well was drilled before drilling the horizontal well. In this pilot well, 360 feet of continuous core was taken and a complete set of modern logs was run and pertinent pressure information was gathered as well. A total of 60 feet of oriented core was taken for a comprehensive analysis in conjunction with the log information and rock mechanical testing. This provided information about the borehole stability which is important during drilling of the horizontal and construction angle section and open hole completion of the horizontal section.
Lower B Sands are part of Misoa Formation of Middle Eocene Age, and in the VLC-100 area they are on average, 600 feet thick. But only approximately the first 250 feet contain net pay and the sands in the rest of the section are saturated with water.