Ok folks i hope this helps you out we’re going to analyze hi basic well log according to petty 1010 the first thing when you look at a well log you should look at the very top to see what logs will run on log number one we see in the lithology track track 1 a spontaneous potential we also see a hydrocarbon indicator however the hydrocarbon indicator is a computed log often computed by a an engineer who has been up for a day two days maybe more without initially I don’t put a lot of credence in the hydrocarbon indicator we do use the spontaneous potential and we’ll talk about that in just a moment the next track – we see there is a resistivity curve or two resistivity curves we use the deep induction curve for our interpretation in petty 1010 because the deep induction curve measures the resistivity of the fluid in the formation in the Virgin’s out in the zone that was not commingled with our drilling flu and track 3 of log one we see the interval transit timethis is a essentially a sonic or acoustic tool which measures interval transit time as it goes through the formation log to in track one which is our lithologies track we have a caliper which measures the size of the hole and we have a camera right the gamma ray is very similar to the spontaneous potential both will help you and help determine where sandstone is or where she’ll is and remember in petty 1010 we’re only dealing with two rocks sandstone or shale the spontaneous potential is a result of an electrical potential which is created by commingling of drilling fluid with formation fluid the gamma-ray measures and natural gamma radiation of the earth and since shale formations tend to hold radioactive material where sandstone formations the radioactive heavier radioactive particles tend to be washed out the sandstones will read a lower rate gamma ray reading then will the shells and then in track 3 and 4 of log – we have what’s called the frosty index we have two curves acog compensated formation density porosity and compensated neutron prosti ok let’s get started with analyzing the log first we’ll look at track one of log 1 the spontaneous potential and will draw a line as indicated by the gold line across the top of the sands we will assume that anything is touching the gold line is considered to be one hundred percent sand and then we’ll draw a green line the Green Line will indicate shale any line touching the shell baseline will be considered one hundred percent shale and of course anything in between the Green and the gold line will be a mixture of sand and shale track to of loved one is a resistivity track and track 3 is an interval transit time let’s draw a line across the top of our zone of interest the black line indicates the top of the sand the second black line indicates the bottom of the sand now in this and it is quite evident by looking at the resistivity curve the deep induction remember that we have some type of hydrocarbon in the formation however the entire formation is not a hydrocarbon formation we have hydrocarbons at the top and we have water at the bottom as indicated by the low resistivity reading therefore as we said in petty 1010 anything above 10 meter for the deep induction curve is considered a hydrocarbon zone the yellow line indicates the bottom of the hydrocarbon zone and reality it is possible to have a much lower resistivity reading and yet have a productive formation and some cases you might have dispersed clays within the sandstone disperse clays which hold water that’s causing the resistivity reading to be much lower than we would expect this would be called low resistivity pay and you learn more about it in petty 30 of course you taken well logging when you’re a junior now when we look at the resistivity though in the zone of interests there’s a hydrocarbon zone I notice that zone which is real high and then the zone decreases so the first thing we need to do is to calculate water saturation water saturation is the square root of r 0 / or tea party is a formation true resistivity in the rear and is the reading from the deep induction curve in the zone of interests are the target zone as i like to say 40 targets up zone of interests true resistivity ro is a reading from the deep induction curve and it clean on Shelly formation fully saturated with it so again let’s set our log up look at the top of the sand the bottom of the sand and the bottom of our productive son now when we’re looking at this and we do notice the high resistivity reading in this zone of interest is 30 however throughout the entire formation the main average of the deep induction is not 30 so what we have to do is we have to calculate two different zones within this zone of interests this hydrocarbons own zone one would be indicated by the red line and that has a 3000 meter reading zone 2 is indicated by the purple line and it has a 20 meter reading therefore let’s calculate water saturation for each of these zones of interests but first in order to do that we must determine ro ro is in a clean one hundred percent wet zone and we calculate or we measure our oh to be . 3 are we sure that that’s a hundred percent water well I’m fairly confident that it is and if you go down the log and you look at the two zones of interest further down the weld the RO from those formations which we assume to be one hundred percent wet would be about the same would also be about . 3, . 3 seems to be a good number for our up so again water saturation equals the square root of r 0 / or tea and this would give us first zone 1a water saturation of ten percent and his own to a water saturation of thirty-nine percent remember the ten percent water saturation in zone one might be water that we will never be able to produce it might be the result of wedding water however the reservoir engineer needs to calculate it into account for it when determining total reserves the next step to evaluate this log is to determine the porosity of the zone of interests the zone that we found to have hydrocarbons frosty equals Delta t minus delta T matrix / delta T liquid minus delta T matrix where delta T liquid and delta T matrix are the transit times in the pour liquid and rock matrix respectively the sonic log investigation is limited to the invaded zone the mixture of liquids in the rock thrower pores is usually assumed to have a transit travel time of delta T liquid of the hundred and eighty-nine selection of the matrix level time delta T matrix is based upon the knowledge of the lithology of the section log commonly used delta T matrix values or as follows sandstone 55.5 microseconds two per foot per foot 51 microseconds per foot limestone 47.5 microseconds per foot and in dolomite43.5 microseconds per foot and the unconsolidated sayings found in south Louisiana for petty 1010 classwork test for delta T use 55.5 microseconds per foot if we were looking at a formation in colorado or Wyoming where the sand stones were well cement it together we might use 51 microseconds per foot again now we looked at the log and what we need to determine is the porosity in the zone of interests if you look at the zone of interest where the hydrocarbons are we see a reading which is fairly close to about 100 microseconds per foot the interval transit time attract 3 goes from 50 to 100 to 150 micro seconds per foot we know however that the sonic law or acoustic log is calibrated in water and if this happens to be a gas formation it’s going to give us of quite a run is reading if it’s a formation containing oil they’re reading would be a run is not quite as bad as if it were in gas but erroneous nonetheless so we go down to the water zone probably where we to pick or Oh from to determine the interval transit time however when looking at our our log arse and our formation that has the hydrocarbons the just below it where we did pick or Oh from we we notice that we’re getting a very inconsistent reading from the interval transit time from the sonic or acoustic log this looks like it might be due to shell stringers it also might be due to the tool bouncing around or are some unexplained noise therefore I prefer to go down to ace and a little bit further down the formation as indicated by the two sands in red and select my interval transit time from these sands I am making an assumption that those sins are homogeneous to the sand in the hydrocarbon bearing zone we will only know that if we shoot sidewall course and have the course analyzed to ensure homogeneity therefore we can calculate prosti from the log again frost equals delta t log minus delta T matrix / delta T fluid minus delta T matrix delta t log is 90 minus delta T matrix 55.5 for unconsolidated  sandstones / 189 which is delta T fluid constant – 55.5 delta T matrix and the frost equals . 2584 26 of course even though our tools might be very sophisticated we’re making assumptions so round off the prosti breathing we have approximately twenty-six percent now the next thing we need to do is to look at track to to look at log – excuse me look at track one to help us further analyze this log right now we know where have I hydrocarbon producing zone we know how many feet of production we might have but we don’t know if we have gas if we have oil and so we’re going to look at the porosity log-log to to help us determine that again now we do not have an SP but we do have a gamma ray and with the gamma-ray we will draw a curve through the top of the sand and a curve through the bottom of the sand and then we’ll look at the frosty curves and we’ll remember the rules that you were taught in class when there is separation such as in the area designated as shale where the neutrons reading high and the densities reading low that’s good indication that we’re in shale when the two logs come together that’s a – good indication that we’re in a liquid do we know if it’s a oil liquid or water liquid no we don’t the only way we know that is by looking at our figure of can order saturation and when the two logs separate when they invert when the neutron read slow and the density reads hi they crisscross from the normal shell reading we know we’re in a gas so if we were to look at our formation we would realize the top of that formation has gas the gas cap the middle of that formation is liquid and we had calculated the worst saturation to be only thirty-nine percent therefore it looks like we have oil with some water of course and the bottom zone again would be a water one other thing I’d like to point out is take a look in track one of love to and you do have a caliper and if you notice in the sandstones the calipers pretty much engaged in the shells the calipers washed out so if I were to ask you I were to give you these logs and ask you at what formation or we end at a particular death tell me all of the indicators that you have you would start by looking at the spontaneous potential you would look at the resistivity you would look at the interval transit time which tends to read high in shells you would look at the caliper you look at the gamma ray and you look at the neutron in density for each of these curves can give you some indication as to what type of formation of what type of lythology you might be in

 

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