PERFORMANCE EVALUATION OF DEEPENED WELLS 420DA AND 517DA IN THE LEYTE GEOTHERMAL PRODUCTION FIELD, PHILIPPINES

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1 PROCEEDINGS, Thirty-Eighth Workshop on Geothermal Reservoir Engineering Stanford University, Stanford, California, February 11-13, 213 SGP-TR-198 PERFORMANCE EVALUATION OF DEEPENED WELLS 42DA AND 517DA IN THE LEYTE GEOTHERMAL PRODUCTION FIELD, PHILIPPINES Rowena N. Abapo, Marie Hazel B. Colo, Romeo P. Andrino, Edwin H. Alcober Energy Development Corporation Julia Vargas cor. Meralco Ave., Ortigas Center Pasig City, Philippines, 165, Philippines ABSTRACT The Leyte Geothermal Production Field (LGPF), located in central eastern Philippines, is a key contributor of geothermal power since its operation in To enhance steam field production, two shallow wells, 42D and 517, were drilled in 24 with depths of 12 m and 17 m respectively. On completion, these wells were poised to meet the steam requirements of the power plants in LGPF contributing a combined output of 4MWe. Well 42D has been producing since 24 until it collapsed in June 27 but was revived through vertical clearing discharge. When 42D reached minimal output in November 21, well was evaluated for deepening with acidizing. This was implemented in May 211 resulting to a gain of 8MWe. Successful deepening of the initially high enthalpy well 42D was achieved by tapping both the shallow two-phase and deep liquid zones of the reservoir resulting to a medium enthalpy discharge. The well also intersected more the Mahiao East Fault and a new structure Litid South Fault in the openhole section providing additional production. On the other hand, 517 was evaluated for re-entry/deepening in July 211 to increase production and clear the mineral deposits, although output has been stable since 28. The minimal increase of 1.6MWe in the post-deepening output of 517DA was expected due to the shallower than programmed total depth cleared and the inability to maximize the target East Fault Line. The LGPF Experience in wells 42DA and 517DA highlighted the importance of the productive structures to be intersected, the well s downhole temperature, enthalpy range, setting depth of the production casing shoe and the length of the openhole section to ensure the improved performance of shallow wells upon deepening. Tapping both the shallow two-phase and deep liquid zones of the reservoir resulting to a medium enthalpy discharge has contributed to the improved performance of the deepened wells. BACKGROUND Upper Mahiao and Malitbog sectors aims to enhance steam field production, hence two (2) shallow wells (W42D and W517) were drilled. W42D was drilled as an intermediate depth well targeted towards the bottom northwest section of W4D while W517 was drilled shallow to tap the shallow feed zones of Malitbog. W42D was spudded on July 1, 24 and was completed on August 2, 24 while W517 was spudded on July 2, 24 and was completed on August 2, 24. W42D tapped the shallow steam zone of the reservoir for production and cased-off Litid North fault which acts as a conduit for injection/condensate returns. In addition, 42D aims to avail the permeability associated with Kapakuhan fault. W517 on the other hand, was drilled to tap the liquid reservoir and target solely the East Fault line. Post drilling tests showed that W42D obtained a modest injectivity index of 18-24li/s-MPa and -3 to - 7 skin suggesting no wellbore damage. W517 obtained an injectivity index of 13.9li/s-MPa with a skin of -3 to -5 which also suggest no wellbore. W517 had been on continuous production since its cut-in on November 24 until it produced minimal output of 1.6MWe in August 21 that made it a candidate for re-entry/deepening. W42D was cut-in on October 24 and well had been on continuous production until it collapsed in June 27 due to injection returns based on gas chemistry. It may also have been influenced by silica deposition, blockage and interference from 423D re-entry. Well was revived through clearing discharge and its ouput recovered to 1.4MWe. Recurrence of the gradual decline in output prompted the recommendation to re-enter/deepen the well.

2 42D sectors. The well s output has been influenced by silica deposition. Well ejected considerable scales (98% amorphous silica) when it was revived through vertical clearing discharge in November 27 after collapsing in June 27. It subsequently recovered its output of 1.4MWe. Silica deposition, caused by extensive boiling of the silica-saturated brine returns is still observed as evidenced by the recurrence of the gradual decline in output to.6mwe as of July21. Another clearing discharge was conducted on April29 but was not able to recover the well s output. This may indicate that silica deposition is not only within the wellbore but could also be within the formation. W42D output is expected to decline further as high enthalpy wells are prone to silica deposition. Figure 1: Location map of W42D 517D Figure 3: Well profile of W42D (pre-deepening) Figure 2: Location map of W517 DEEPENED WELLS Well 42D deepening W42D was originally designed to be sidetracked from the original total depth of the well at 12mMD. However, the liner retrieval operation recovered only 221 m of the slotted liners and not the entire length. Hence, the sidetrack point was revised from 12 to 932mMD. W42D attained the target depth of 23mMD without major problems encountered during drilling/deepening. W42D data and profile The well is a shallow in-fill production well drilled to augment the steam supply for the steamline interconnection (SLI) that diverts steam from Upper Mahiao sector the Malitbog and Mahanagdong Figure 4: Well profile of W42DA (post-deepening) Figure 5 shows the W42DA fluid chemistry trend. Cl res level increased to 1,ppm-12,ppm while

3 Tqtz increased to 285 C. C 2TD is stable at 5 mmol/1mol after the deepening. associated with East Fault Line. W517 output is relatively stable since 28 at MWe. Figure 6: Reservoir Process affecting 517 Figure 5: W42DA Chemistry Well517 deepening Well 517 target depth was supposed to be at 27mMD. However, due to recurring high torque and increasing pick-up weight, well was completed at a shallower depth. During deepening, well was sidetracked through the 9-5/8 production casing between 131 and 137mMD. The 7 TOL was set at 997mMD, while the 7 BOL was squatted at the bottom. Circulation losses encountered between 1439 and 12mMD. Drilling blind down to total depth had caused poor hole cleaning resulting to recurring tight holes, obstructions, fill and stuck pipes. In the 8-1/2 hole, the well track bit walked within the East Fault Line at 1249mMD and further made a positive walk between 1278mMD and 213mMD of Kadluman Fault. A low drilling penetration rates of 1.9mph was observed during at mMD, thus the hole was prematurely bottomed out at 243mMD. Slight decline in its output was observed as compared to its earlier discharge in 25 which can be attributed to the effect of injection returns as confirmed by the positive tracer responses from injection wells. The re-entry was recommended to recover its output and clear the hole of mineral deposits. W517 data and profile W517 was a shallow vertical well at pad 511 of the Malitbog sector. It was drilled to a total depth of 17mMD. The well has an output of 2.7MWe but due to reservoir pressure drawdown, the well s output significantly decreased to 1.6MWe. The re-entry sidetracking and deepening of the well was considered as M & R well owing to the limited areas of expansion in the Malitbog Sector (Bien, 211). The well was drilled to supply steam to the Malitbog power plant and tap the liquid phase of the reservoir existing at deeper levels below -435mRSL for production and to intersect the permeability Figure 7: Well profile of W517(pre-deepening)

4 Figure 8: Well profile of W517DA(post-deepening) Figure 6 shows the W517DA fluid chemistry trend. Cl res level is still lower compared to its pre-deepening level while Tqtz increased to 26 C. Measured downhole temperatures of the two wells (Table 1 and 2) are above 22 C. Well 42DA (Kh=23.5da-m) showed better permeability than W517DA (Kh=3.2da-m). Furthermore, W42DA had better acceptance with an injectivity index of 133li/s/MPa compared to the 48li/s/MPa injectivity index of W517DA. DEEPENED WELLS PERFORMANCE The pre-deepening outputs of wells 42D and 517 are presented in Tables 3 and 4. The output of W42D significantly increased after the deepening from 1.6 to to 9.MWe (June 211). There was a similar but not as significant an increase in the output of 517 after the deepening from 1.6 to 3. MWe. Figure 6: W517DA Chemistry Table 1: W42D Pre and Post-deepening output Predeepenindeepening Post- Max Measured Temp C 279 (12mMD) 281 (2mMD) Injectivity Index (li/s-mpa) Kh (da-m) Major Permeable Zone,mMD Table 2: W517 Pre and Post-deepening output Predeepenindeepening Post- Max Measured Temp C 245 (169mMD) 246 (22mMD) Injectivity Index (li/s-mpa) Kh (da-m) Major Permeable Zone,mMD 16 - Table 3: W42D Pre and Post deepening output Predeepening Postdeepening % Output Increase WHP (MPag) MF H (kj/kg) % SF MWe COMPLETION TEST DATA W42D completion test results (Table 1) show that major permeable zones are located at 85-97mMD before and after the deepening. The major zone at W517 is at 16mMD (Table 2) although this is not apparent after the deepening.

5 H (kj/kg) H (kj/kg) Mass Flow Water Flow Steam Flow Mass Flow Water Flow WHP (MPag) Steam Flow WHP (MPag) lrmd/lgpf/rna 3jul12 W42D Output vs Time 42DA deepening to its target depth. The well was also able to intersect additional structures, i.e. Kapakuhan, Mahiao East and Litid South. Improvement in the well s injectivity index from 24 to 133li/s-MPa suggests enhanced permeability and acceptance. The well s downhole temperature is also relatively high from 279 C (pre-deepening) to 281 C (postdeepening), which also contributed to the well s performance given the high enthalpy nature of its discharge Figure 7: W42DA pre and post-deepening output Table 4: W517 Pre and Post-deepening output Predeepening Postdeepening % Output Increase WHP (MPag) MF H (kj/kg) % SF MWe Figure 8: W42D pre- deepening temperature W517DA Output vs Time 517DA DR =.2MWe/mo Figure 9: W42DA post- deepening temperature Figure 8: W517DA pre and post- deepening output lrmd/lgpf/rna nov11 The significant increase in the W42Da postdeepening output maybe attributed to the successful The minimal increase in the 517DA post-deepening output was due to its premature completion at a shallower depth (243mMD). Hence, the target East Fault line at 27mMD was not bottomed out. Bitwalking at the fault plane did not contribute much to the well s output. No significant improvement in the well s temperature was observed (245 C to

6 246 C) and its post-deepening condition may have affected the well s output. With the well deeper, there could be more contribution from the liquid zone as evidenced by the increasing water flow during TFT measurements. There was a significant increase in injectivity index from 13.9 to 48li/s-MPa. SUMMARY Well 42DA has tapped both the upper two-phase and deep liquid zones of the reservoir resulting to a medium enthalpy discharge. The well has also intersected more the Mahiao East Fault and a new structure Litid South Fault in the openhole section providing additional mass inflow for production. W51DA improved its post-deepening output from 1.6 to 3MWe. A higher liquid fraction in the discharge resulted from the deepening. For future deepening of shallow wells it is recommended to consider the prolific structures to be intersected, high downhole temperature, high enthalpy, dry well and the reservoir condition in evaluating candidate wells for deepening to produce significant results. Application of new technologies to enhance the well permeability and productivity can also be evaluated. Figure1: W517 pre- deepening temperature REFERENCES Bien, O. C., (211), "Geological Report of Well 42DA, Pad 47, Tongonan Geothermal Production Field, Leyte. Energy Development Corporation (unpublished) Bien, O. C., (211), "Geological Report of Well 42DA, Pad 47, Tongonan Geothermal Production Field, Leyte. Energy Development Corporation (unpublished) Figure11: W517DA post- deepening temperature