IMPROVEMENT OF ANALYSIS VERTICAL OIL

EXPLORATION WELLS (CASE STUDY)

Prepared by : Eng Azza Hashim Abbas

Supervisioned by : Wan Rosli Wan suliman

WHAT IS A WELL TEST? A tool for reservoir evaluation and

characterization Information obtained from flow and pressure transient tests about in situ reservoir conditions Investigates a much larger volume of the reservoir

than cores or logs Provides estimate of permeability under in-situ

conditions Provides estimates of near-wellbore condition Provides estimates of distances to boundaries

HOW IS A WELL TEST CONDUCTED?qq = 0

t

q

t

p

CASE STUDY Introduction Objectives About the field About the wells Geological formation Fluid properties DST Analysis Results

INTRODUCTION TO CURRENT PROBLEM

Operator companies regularly development new fields without extensive evaluation

in many cases, predicated reserves and actual were very different Reservoir engineer needs to be careful in interpreted the routine (DST) .

There is no single method of testing and sampling that is fit for purpose under every circumstance.

SUDANESE FIELDS The Sudanese field in the west encounters immense risks,

notably, the uncontrollable armed movements of the rebellious tribes

The geological nature of the land and the heterogeneity of the petro logical layers.

A standard DST operation has been run for three days without a previously prepared design for the operation sequence, which should have been based on the field situational characteristics. The Moga field was located in the west when it was discovered at the beginning of 2003.

It was a promising location. Well 22 which was performed as an exploratory company very careful in dealing with Well 22 which had an immense challenge to complete and perform the relevant tests, especially, when the test results were not favorable for later studies as routine analyses somehow led to misleading results.

PROBLEM ASSOCIATE WITH ROUTINE TEST

To get reliable description of petroleum reservoirs accurate estimation of the skin factor, PI and the true layer rate of flow is very important . Over estimate of PI cause fulse prediction about the deliverability of the laye

By following certain steps as avoiding the pressure noise- that damages the first part of the data -,by introducing a new gauge that is compatible with the original back-up gauge and, to introduce the deconvolution method in order to complete the analysis with better results. The result accuracy will be improve

CONVENTIONAL METHODS

There are two ways in which the properties can be estimated. For both methods the step response has to be plotted.

The first method is a direct interpretation of the Horner plot.

The second one is a method in which the plot of the well test data is compared to plots of known properties, the type curves. By matching, the reservoir properties are estimated

DECONVOLUTION METHOD

the aim of deconvolution is to calculate the impulse response of the system, based on the transient pressure response and the flow rate. In well-testing literature,

there are, however, various definitions of deconvolution used. Methods to extract the impulse response g (t) based on the input and output is deconvolution methods

CASE STUDY OF NEW FIELD (MOGA FIELD)

Well and reservoir overview:

Well-Testing Reservoir Parameter

After reading through all the well-22ports (geological, fluid properties, completion reports), the input data was then extracted as

Well type: Vertical exploration well

Test zone: Abu Gabra

Interval: 1633.0-1635.0 mKB

Parameter Value Total thickness 2m Porosity 0.21 API 18.97 Test type STANDARD

CONVOLUTION ANALYSIS

Saphir software has been used for the previous data to get the history plot, which is also the Cartesian plot of production, and pressure data versus time in which a model is generated, the simulated response is shown.

By loading pressure gauges data, it can be seen that the noise distract the first area as shown

Two gauges were loaded The presence of regular distribution points were caused by mechanical issues wherein the difference between the basic gauge and the back-up gauge caused a confusion where instead of choosing which one to work with it was better to create a new test.

Using the gauge difference in reading, it was possible to get a new gauge calibrated between the original gauge and the back-up gauge, which solved the problem partially.

The simulated semi-log also cannot give enough points in the middle time region of the reservoir. It seems that the semi-log does not stand in the proper area due to the lack of data and risky results and the process of crosschecking of the permeability and the skin factor from the simulated semi-log with the simulated history and derivative will be a sheer waste of effort.

RESULTS

Property Value Pi 14.155 S -3.81 Ko 21.6

DECONVOLUTION ANALYSIS

By using the available data extracted from the deconvolution process and modeling exercise, the assumed model based on the same previous data gave the characteristic features and attributes of a homogeneous reservoir but with a parallel fault, all of which show more appropriately authentic results in the simulation process.

After generating the pressure and reservoir responses, the IARF then appears in short sequences, which can be detected easily from the chosen reservoir area that provides better results on the reservoir characteristic properties for gainful usage at a later stage

RESULTS

Property Value Pi 13.892 kpa S -3.98 Ko 26.6

DISCUSSION

the characteristic damage as fracture damage. The change in the determined values of skin

between the convolution and deconvolution can be neglected.

The variation of range of the initial reservoir pressure between the two methods is within acceptable limit.

However, the reservoir permeability cannot be obtained from the convolution process because the data does not represent the reservoir. On the other hand, the deconvolution method has given a better result after using the condition of a parallel fault even though it does not give a very close result with the circle result

CONCLUSION

Oil exploration areas often encounter critically dangerous situations of uncertainty if the interpretation of preferred oil thickness is applied but the uncertainty factor can be considerably mitigated if calculated option can be made for the other dip exploration well by estimating the existence of a possible nearest fault and heterogeneity change for each layer

THANK YOU

QUESTIONS