A New Method for the Evaluation of Well Rehabilitation from the Early Portion of a Pumping Test

Round 1

Reviewer 1 Report

The article  "New Method for Evaluation of Well Rehabilitation from the Early-Portion of the Pumping Test" by the authors Daniel Kahuda and Pavel Pech is an interesting contribution to the assessment of the well's hydraulic efficiency, especially  using short hydrodynamic tests.

The analysed manuscript is written correctly, but in my opinion the summary should be improved in the context of a more complete presentation of the new elements contained in the paper also keywords should be improved.

The literature review is wide, but there is a lack of analysis regarding the impact of drilling mud on damage of the aquifer permeability in the near-well zone during drilling operations and the impact of hydrochemical processes occurring in the near-well zone during well exploitation on water flow resistance in the filter and filter zone.

It seems that the authors in this context should change the content of the sentence regarding the range of the skin zone (lines 53 and 54).  The range of permeability damage of aquifer rocks during drilling operations with drilling mud is rather from a few millimetres to several centimetres.  Whereas permeability damage of aquifers of a larger range (up to several meters) is caused by physicochemical and biological processes occurring during well exploitation.

The rest of the manuscript is written correctly and the conclusions contained in the final part of the paper are correct.

Before the publication of this manuscript, the quality of the drawings should be improved, especially Fig. 1 and Fig. 10. Furthermore, the diagram of the well (dug well S-V) shown in Fig. 10 is not well understood by the reader and should be corrected.

Author Response

Thank you for your review.

Responses to comments in the review

1. changes were made in summary and also in keywords
2. new literatures were added   … "impact of drilling…" (52, 53 and 54)

                                             …. "impact of hydrochemical ….." (55,56 and 57)

   3. lines 53 and 54 (range of skin zone) were changed

   4. Figure 1 and figure 10 were exchanged 

Please see the attachment - where you find changes 

Reviewer 2 Report

The authors propose a new method for evaluation of skin factor from early-portion of a pumping test, which they suggest to be applicable also to the interpretation of pressure drawdown and build-up test, widely used in the oil&gas context. The paper is well organized and the scientific soundness is good. The effort made to extend the audience of readers to petroleum field, through references to the petroleum literature, methods and terminology, is appreciable. However, to fully reach this goal, additional disambiguation and further discussions are necessary here and there. More in details:

Introduction:

1) The introduction claims to report an extensive well test history of both hydrology and petroleum fields; the reference list on petroleum sides is quite complete, but not supported by an adequate discussion of the methods. For instance, among the mentioned method the authors missed to describe the derivative approach by Bourdet et al (1983, ref. 35) which allowed an impressive improvement in the resolution of the assessment of wellbore storage and skin with respect to the 1970’s log-log type-curve matching techniques; it is the basis of the modern well test analysis in the oil&gas context (ref. 3 and ref.5), as well as the core of oil & gas well test commercial softwares. Moreover, based on such approach, many models were developed over the years to cover different scenarios (radial composite, closed boundary, wells intercepting a fracture, partial penetration, horizontal well, ... ). It is quite surprising that ref. 3, ref. 5 and ref.35 are reported but the methodology is not mentioned and just liquidated it as one of the “Other type curve methods” (line 63-64) for which, according to [10], which is older than most of the referred methodologies [35-42],  “It was showed that principal problem with application  type-curve methods is similarity of the shapes of the curves mainly in the early times of pumping and that is problem to obtain quantitative information with as much precision as with conventional Cooper-Jacob semilogarithmic method for late times” (lines 64-67).

2) The given well test definition (lines 22-23) is quite different from the oil&gas world in which what is measured and analyzed is the pressure. The use of term “drawdown” could also be confusing. In fact, in petroleum literature it refers to the well test flow period characterized by a pressure drop. A disambiguation is recommended , as well as a discussion of the applicability of the cited petroleum literature methods when the measured quantity is not pressure but water level.

Conclusions:

line 462:“The new technique is applicable to the interpretation of pressure drawdown and also build-up  test.” Some discussion is needed, for instance a comparison in terms of pros and cons with respect to the well established derivative approach (Bourdet el ta. 1983, ref. 35). Moreover, some more details on the application of the presented methodology to pressure data should be given.

Some minor issues:

line 62: “lo-log” should be corrected by “log-log”

line 266: “W” was not previously introduced and its meaning is not explained. A nomenclature list is also absent.

line 449 “data from a it is necessary”: something is wrong in this sentence

Author Response

Thank you for your review.

Responses to comments in the review:

1. In section "Introduction" the part with type curve methods was rewritten (lines 75-101 - in the attachement)
2. This article deals with groundwater hydraulics where "drawdown" in the well is defined as difference between the height of water in the well before start pumping and the actual height of water in given time (we changed lines 22-23 …. newly lines 27-31, which can contribute to clarification groundwater x petroleum "field tests"
3. Section "Conclusions" - build-up tests were eliminated in the text

       lines 501-523 were added for eventual application article´s results in 

       petroleum area

   4. Minor issues:

       line (62) "lo-log" was changed to "log-log"

       line (266) -"W" was changed to skin factor "S_F"

      line (449) - sentence was changed

Please see the attachment

Round 2

Reviewer 2 Report

I appreciated the effort put by the authors to address my comments. Only the comparison in terms of pros and cons with respect to the well established derivative approach (Bourdet el ta. 1983) is missing, however the made revisions improved the paper significantly.

Some minor issues related to the made corrections:

lines 27-31: concept are now perfectly clear. However, the sentence is very long and a bit hard to read. I suggest to rephrase.

line 87: “pressure derivative as the derivative of dimensionless pressure with respect to dimensionless time/dimensionless wellbore storage”. This is not completely correct. Pressure derivative is defined a s the derivative of dimensionless pressure with respect to the logarithm of dimensionless time (see eq. 2.28 in Bourdet , 2002 Well test Analysis, the use of advances interpretation models).  Why divide by wellbore storage in the derivative definition?

line 92: “Bourdet and his co-authors proposed that flow regimes can have clear characteristic 91 shapes if the “pressure derivative”, than pressure is plotted versus time on the log-log coordinates.” This is not completely correct. Pressure and pressure derivative are plotted versus time on the log-log coordinates.

lines 99-100: “Even if there is no qualitative analysis possible the derivative may give some qualitative information about the aquifer.” I did not get the point in this sentence. It must be clarified.

Some typographical errors:

line 27: “well testingare” -> well testing are

lines 81, 82, 85 and 610: “Gingarten”-> Gringarten

line 96: “tis”-> this

line 495: “..”-> .

Author Response

Thank you for Your review and comments.

Responses to comments:

lines 27-31 ... definition of groundwater test has been changed

line 87 ... we deleted "dimensionless wellbore storage"

line 92 ... the sentence has been slightly modified

lines 99-100 ... the sentence "Even ........." has been deleted

typographical errors:

line 27 "well testingare" ... has been repaired "testing are"

lines 81, 82, 85 and 610 ... has been repaired to "Gringarten"

line 495 ... one "." has been deleted

Please see the attachment

Author Response File: Author Response.docx