INTRODUCTIONAn isopach is a line representing equal stratigraphic thickness, and an isopach (or isopachous) map is one that shows by means of isopach the variations in true stratigraphic thickness of a stratum, formation, or group of formations. The subsurface isopach map is based primarily on formation thicknesses determined from well cuttings, cores or geophysical logs. Although isopachs must be drawn to agree with thicknesses plotted on the map, their spacing and the nature of thickening and thinning may be guided by other known facts concerning the source of sediments, their relative rates of deposition, truncation, and so forth. An isopach map drawn strictly to the numerical values and without regard to the geologic reasons for thickening and thinning of formations, is likely to present a picture difficult to integrate or reconcile with other geologic facts.

Figure : Structure map and corresponding isopach of the producing interval.Two methods will be applied in this lab to estimate volumes from an isopach map. The first will be to use a planimeter to estimate the average thickness within the isopach area. The second method utilizes a software package that includes digitizing the isopach map and applying geostatistics to determine the volumetrics.When a map showing contour lines (isopach) is available, it is possible for us to then measure the area of each reservoir. This process is called planimetry. Planimetry measures the area of the property. Therefore,with the area and thickness know,a volume of reservoir can be calculated,and from this,a total tonnage can be deprived. Planimetry can be done by hand using several methods but the one we are using in this experiment is a mechanical device called a planimeter. Planimeter, also known as platometer is a measuring instrument used to determine the area of an arbitrary two-dimensional shape.In addition, planimetry can also be done accurately by a computer using special software. The gross reserve estimate can be calculated from the calculated areas and the projected thickness trends. However, if we want to determine what the oil in the reservoir is worth, there are many other factors that must also be examined such as quality, mineability, transportation, available market and lots more..Nevertheless, we are only concerned about the ability to calculate the volume and capacity of a reservoir in this experiment. In simple words, volume is the amount of space taken up by an object, while capacity is the measure of an objects ability to hold a substance, like a solid, a liquid or a gas. Therefore, isopach and planimeter were the only things that came in handy to help in completing this experiment and we were able to use the value obtained for the three methods that we had used to calculate the volume and capacity of each reservoirs.

SUMMARYIn the fifth experiment, our group has to conduct an experiment about the volume and capacity of a reservoir in map by using a device call planimeters. As we all know, the objectives of this experiment is to determine the capacity of oil reservoir based on the isopach map and thus the original oil on place (OOIP) of the reservoir can be calculated.A contour map of a reservoir was prepared and ready to determine the area of the reservoir which stored hydrocarbons. Planimeters didn't calculate in the sense of allowing a user to enter some numbers and producing a result. They did, however, solve a tedious and common problem - that of determining the area of some closed shape. In other words these devices were integrating machines.To use a planimeter, our member will set up the device, zeroed the recording wheels and then traced the pointer all the way around a closed shape from the starting point that we had marked (typically a clockwise direction was used to produce a positive result.) The area could then be read directly off the dials. Better planimeters allowed adjustments to allow the device to read in various units and scales. Other units simply read in a fixed scale such as square centimetres and required the results to be scaled to the units required. The results or the readings were then tabulated in a table provided and calculation can be made in order to find area or capacity of a reservoir by multiplying the area and the depth/structural elevation of the reservoir. Overall, the objectives of this experiment we had succeed to achieve it.